Seems like you’ve got the idea now!
Most people should target 15-21 minutes here. Up to 24 or 25 max for these sessions. I’ve personally only ever done one 24 min set on a day where I felt really good. I normally am 20-21 minutes myself, so there’s no shame in ditching the last interval if you’re wiped out.
For those keeping track at home, that would be:
3-4x6min
3-5x5min
4-6x4min
5-7x3:30
6-8x3min
Those are my usual prescriptions and how I structure them depends on the athlete and the block style they’re doing. I usually give a range like that, and the goal is the middle value. Feel great? Do the max. Gassed? Do the minimum.