Try it and see. You are going to have varying abilities (both power and recovery) and varying draft potential. For a 4 person TT, how much you can rest in the line depends largely on how much air you push compared to the person in front of you - if they are tiny and you are large, there isn’t going to be much resting going on at all.
It’s also worth practising starting with different people in different positions. I would suggest slowest to fastest, but that can lead to the slowest person struggling to get on the back after they have started everyone else off. It depends on how the rotation works out as well.
Practising is really useful. Also, working out what words you want to use to communicate beforehand - make them short and different - if you use “go” and “slow”, there’s going to be an issue!
Edit - when we’ve done 9-up TTs, 20-30 seconds is a good length for a pull. You might find that doesn’t give enough “rest” time for a 4 up.