I am no expert, but I will throw in my two cents. I am on a hybrid schedule this year, 55 minute periods M, T and TH. I do one core lift and two accessories on these days for the most part. We have no more than 3 in a group. I feel like that is enough rest until we get up to our heavier sets, then I slow them down a little bit. We go on the whistle, so it is not hard for me to do so. I will usually take some extra time to throw out some reminders and cues and then get them going. The only thing I time is push ups, we go for a certain amount of time and if they burn out before that time is up, they must maintain good push up position for the remainder of the time. Hope this helps.