Guide
How long to rest between sets
Rest is part of the program. Two people who both 'do 3x5' are not doing the same workout if one starts the next set at 45 seconds and the other chats for four minutes. Write the rest down, or at least time it.
Ranges that match the goal
For heavy strength sets, something like 3 to 5 minutes is common because the next set is supposed to be heavy again, not a conditioning test. For moderate hypertrophy work, 1 to 3 minutes is a usual band. Short rests, under a minute, fit finishers and some supersets, and they change what the weight means.
These are ranges, not a law. If the next set falls apart, you rested too little for the load you wanted. If you are reading email between sets of lateral raises, you are no longer training the thing you wrote down.
Time it the same way every week
In TrackYourLift, completing a set can start rest on its own. That is the right moment, because the argument about whether rest started 'when I racked it' is how logs get sloppy.
Racked is the separate rest interval timer for iPhone and Apple Watch, from the same developer. Use it when you want a timer and not a log: warmups, a metcon station, or a gym day you are not tracking in TrackYourLift. It is not a workout journal.
Racked on the App Store: https://apps.apple.com/us/app/racked-rest-interval-timer/id6822546484
Supersets and the lie of the clock
In a superset, the rest that matters is often the rest after the pair, not the three steps between the two exercises. Decide which interval you are timing before you start, and use the same rule next week.
Should rest be the same for every exercise?
No. A heavy squat and a rear-delt raise do not need the same clock. Time the sets whose load you are trying to progress.
Does the Watch app time rest by itself?
The Watch app needs the iPhone nearby. Rest during a TrackYourLift workout is part of that session, not a watch-only timer you start on a run.