My personal favourite: https://english.stackexchange.com/a/593667
Down to the wire
full of suspense
especially : unsettled until the very end
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.
- crunch and chop are great verbs if you want to emphasise risk of failure to meet the deadline.
- crunch time is also used to describe scenarios of high pressure that might not necessarily be associated with a deadline, it is more of a statement of the current situation and less about what might be coming.
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.
- The butcher is probably not going to wait a whole hour before chopping...
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.