I opened a support call on this over a year ago, and since then I've kind of just dropped it because I assumed it would be addressed in a future firmware update. Unfortunately over a year later, this is still missing, and and I'm not really sure why no one ever seems to complain about it.
When doing 'self made' workouts, as opposed to a Garmin suggested workout, if you try to set up a data screen to guide you through the work outs intervals and step timing, there should be field available under 'workout fields' called Step duration. It exists in the Garmin 955 (wife and one kid have this watch), but is a noteable ommission in the Epix Gen 2 watches, and I'd have to assume the Fenix line-up as well.
This field counts down the time remaining in the current step. So if you are warming up until lap press, it would 'until lap press'. If you were doing a 45 sec sprint, once the sprint started it would count down until 45 sec elapsed, and most importantly, when you are in a rest interval you can see the time remaining until the start of the next interval.
Oddly, this field clearly exists within the watch because if you do a Garmin Suggest workout (running or cycling), that field is part of the default screen you see when you do the workout, selected by Garmin by default.
Why would this be missing on such a high end watch? Is it on the Fenix 8? I wouldn't upgrade without knowing this as I would use it regularly, and I'm just a frustrated regularly by the fact that it is missing!
When I called support a year ago to try to find out if they renamed it of put it into a different folder of data fields, the most useless rep discovered there was no work-around, and no follow-up on if and when it would be addressed. I wanted to document in this forum so other people know they aren't crazy when they try to setup custom workouts and can't figure out how to do this!