If I need to talk about the concept of the switching between daylight saving time vs non-daylight saving time, is there a term specific to that?
I can say something like "Tomorrow, we'll change timezones." or "The misunderstanding on delivery time was a timezone issue." because things like EST and EDT are technically timezones (according to IANA), but that word seems too broad and also connotes more a difference in time by geography rather than time of year.
The Wikipedia article on Daylight Saving Time uses a few nouns to describe this category. I would scarcely consider any of these "standard" but here is evidence of how people have previously addressed your problem.
clock shifts
DST clock shifts sometimes complicate timekeeping and can disrupt travel, billing, record keeping, medical devices, heavy equipment,[5] and sleep patterns.[6]
The relevant authorities usually schedule clock shifts for, or soon after, midnight and on a weekend to lessen disruption to weekday schedules.
time manipulations
The manipulation of time at higher latitudes (for example Iceland, Nunavut, Scandinavia or Alaska) has little impact on daily life, because the length of day and night changes more extremely throughout the seasons (in comparison to other latitudes), and thus sunrise and sunset times are significantly out of phase with standard working hours regardless of manipulations of the clock.[16]
time regulation (This is more of a stretch – the author does not use it as you intend – but is a reminder that daylight saving time is a policy.
In 1810, the Spanish National Assembly Cortes of Cádiz issued a regulation that moved certain meeting times forward by one hour from May 1 to September 30 in recognition of seasonal changes, but it did not actually change the clocks.
Clock shift is used most frequently in the article and, in my judgement, is pretty intuitive. It does not very well describe jurisdictions which permanently have switched to DST, but in those cases timezones probably fit better anyway.
Daylight Saving Time will be referred to as DST from this point onward. In the UK you'd say "summer time"
For lack of a better term that encompasses both concepts, you could say "we're changing our local time tomorrow", which can mean that we are either "getting back to standard time." or "going on DST as of March ...."
or, "Time Category" (DST or Standard?) seems like a better fit, though.
Wikipedia has an excellent article about DST.
Both of the following sentences could be going either forwards or backwards:
Tomorrow, we'll change our clocks.
The misunderstanding on delivery time was a daylight saving issue.
There's no single word or phrase to cover every example. The closest is "daylight saving" since equatorial timezones don't have daylight saving time. Either you have standard time all year round or you alternate between standard time and daylight saving time. You could also say:
Tomorrow, there's a daylight saving change.
