Good question. Of the three coaches in our team I tend to be the one that wants to move on quicker. I'd say 10-15 mins per drill (so 4-6). I do though consider how the kids are reacting. If I'm losing them I'm move on quicker maybe and come back later

I would go with three personally. 

Arrival/Warm up Activity - 10 mins

Main Activity (with progression) - 30 mins

Game (with constraints if appropriate) - 20 mins

I have squeezed in two main activities in the past and tend to always have one up my sleeve. Main thing is to be flexible though.