I want to say something like,
I am getting down to the chopping block
but that means more like, I am deciding who to keep and who not to, it conveys being harshly decisive.
That's not quite the point. The point is that as you approach the final hour, things get tense, yet exciting.
Is there a similarly colourful expression of the form, "I am getting into/down to...." ?
You can use the idiom (be) in/on the home stretch. I believe it is used as home straight also in the UK.
In the midst of the final portion of an activity, project, competition, etc. Likened to the straightaway at the end of a race.
The bulk of the work is behind us—we're in the home stretch now!
idioms.thefreedictionary.com
The analogy comes from horse racing, and home stretch is a term used in baseball also.
You can say
It's crunch time.
It's coming to the crunch.
Farlex has
crunch time
A critical period of time characterized by a heightened pressure to succeed, usually at or near the end of a given situation or undertaking.
A period when pressure to succeed is great, often toward the end of an undertaking.
Okay, we've got two minutes to tie the game—it's crunch time, guys!
Another suggestion is
We are coming to the moment of truth.
Farlex says
The moment or point at which some critical and decisive event, action, or test will occur.
We've been working on a prototype of this device for months. Now comes the moment of truth, when we test it in a real-world environment.
An idiomatic expression for that would be: down to the wire.
Were you to say, "I'm really taking it down to the wire," you'd be saying that you're getting quite close to the deadline, even possibly ill-advisably close or dangerously close -- so close that you very well may not get it done in time, especially if any unforeseen problem or unforeseen delay arises, as "taking it down to the wire" means you're leaving yourself no extra time at all for anything except exactly what you expect needs to be done at the fastest pace you're estimated capable of doing it in, which it's quite possible is an overestimation, another common cause of people taking it down to the wire missing their deadlines and why taking it down to the wire is so close to the end of a time-sensitive project that it can even end up being too close.
What is an expression you can use for when you're getting close to the end of a time-sensitive project?
^ This is a bit ambiguous. Are you close to the end of the project or close to the end of the time constraint?
If you are at the end of the time constraint then:
I am in the eleventh hour
: the latest possible time before it is too late
// still making changes at the eleventh hour
If you are close to completing the project then:
I can see the light at the end of the tunnel
A light at the end of the tunnel
: a reason to believe that a bad situation will end soon or that a long and difficult job will be finished soon
// They are falling deeper into debt, and there is no light at the end of the tunnel.
// The work on our house has been going on for months, but we're finally starting to see a light at the end of the tunnel.
If both then:
I am in the eleventh hour but can see a light at the end of the tunnel.
You could use an expression from horse racing...
I am getting into the final furlong.
Where the final furlong is the last ⅛ mile (0.2 kilometer) up to the finish line...where things get tense, yet exciting.
It’s showtime. The preparations and rehearsals are over. It’s time to put your work in front of the paying audience.
This concept of putting on a show is also used in the term show stopper. As in: “We’ve still got lots of problems, but no show stoppers. Let’s go ahead with the release”.
"Squeaky bum time"
This is my personal favourite. Possibly invented by former Manchester United boss Sir Alex Ferguson. It has also been used in Doctor Who. It fits perfectly the usage you are after. Time is running out, things are getting tense.
Another colorful idiomatic expression is down to the short strokes as it appears to be an allusion to painting. A painter starts painting on a clean canvas using large or broad strokes of the brush; but as the painting progresses, the strokes become shorter and finer where the painter fill the details into the painting. It reminds me of Bob Ross where he paints twigs and sticks at the end of his paintings, whether on the happy trees or within the nature that you can see in almost all his paintings.
Wiktionary also adds that it can be an allusion to golf or swimming; and provides the etymology and the definition as below:
Etymology: Possibly an allusion to painting, in which a painter typically finishes a work with short, careful, finishing strokes of the paint brush, or to golf, in which a player concludes each hole by making short strokes with a putter. In swimming competition, as a swimmer nearly reaches a wall to turn or to finish, the competitor might take a shorter stroke to start the turn smoothly, or to finish faster.
Adjective
down to the short strokes
(idiomatic) In the final steps or decisive phase of an undertaking, especially one which has been lengthy or laborious.
My personal favourite: https://english.stackexchange.com/a/593667
Down to the wire
https://www.merriam-webster.com/dictionary/down-to-the-wire
full of suspense especially : unsettled until the very endhttps://knowyourphrase.com/down-to-the-wire The phrase down to the wire means that there is a tense situation in a competition where the outcome is only clear at or near the end.
It’s believed this expression originates from horse racing, but why? Because in horse races, a wire was often hung across the finish line in order to help determine the winner. This was especially useful in races that were very close towards the end. Thus, as the riders approached the finish line, they could be described as coming down to the wire, quite literally.
Different subject domains and the urgency or likelihood of meeting the deadline will lend themselves to different phrases.
I like It's crunch time however this implies a more imminent and yet less predictable deadline, which is similar to being on the chopping block.
To help put some of these phrases into context, I am guilty of over-using pep talks like this as we approach the end of a milestone or a competitive sport:
It's crunch time people! We're in the final straight but I don't want this one to come down to the wire!
in the Eleventh Hour is similar to the previous phrases, still with a close but not literally fixed deadline, without the same immediacy.
moment of truth and It’s showtime both allude to a reveal, which is still exciting and inspires anticipation but is past or present tense of the deadline, so less about the preparation or the amount of time that is left.
I am sure there are other idioms that apply to this scenario but there are many metaphors at our disposal. The problem with a metaphor is that you need to be aware of your audience and be careful to use a comparison that the target audience is likely to be able to relate to.
When using a technical domain reference (like down to the short strokes) the message can be ambiguous to a reader who does not understand the domain, even if the reader can surmise the intent based on the common setup down to XXXX, the emphasis that you are trying to make about excitement and tension can be easily lost.
Sporting references are similar except that they tend to be geographically or culturally constrained or will have slightly different variations that might make it hard for the reader to relate to. The examples offered by @Davislor highlight some of these variations.
Overall it would appear that horse racing analogies are over represented in this scenario, but that is likely due to it being a relative standard sport across many English speaking regions that have traditionally involved all castes and classes of society in different ways for many centuries. So its generally a safer sporting reference to use as there is a high chance that an English reader would be able to relate to it.
Merriam-Webster defines buzzer-beater as:
a shot successfully made just before a buzzer or horn sounds to signal the end of a period
especially : such a shot made to win a game just before the final buzzer or horn sounds
A closely-related expression is at the buzzer.
Some of many other metaphors from sports: bottom of the ninth (from baseball), inside the two-minute warning (American football), stoppage time (soccer), at the death (primarily British—American soccer fans seem familiar with it from British announcers, but be careful with this one), sudden death (many sports, but again, be careful that this is clear in context) or match point (tennis).
One other option is "getting into the short rows." This comes from farming; if you are plowing a field that is at all irregular, the last few rows will be shorter than the bulk of them. It's a good metaphor for all the little tasks that often have to be done as a project is wrapped up, and so it's not the same as "crunch time", which suggests that central tasks are being worked on right up to the end.
I would also distinguish "crunch time" from "the home stretch". The former has a stronger sense of pressure (after all, the word "crunch" is right there in the expression). The latter, for many people, focuses on being close enough to the end that you know you will finish. Of course, in a horse race that is a very high-pressure time since you want to win the race, not just finish, and maybe you're not even leading. But in practice, people often talk about being in the home stretch when a lot of the risky parts are done and they are feeling more confident.
