You can take as short or as long a rest period as you need, although beyond 3 minutes it is doubtful if the rest period will actually do more good.
Changing between muscle groups, you may opt to not rest at all and just superset them.
The best advice overall is "listen to your body". If between sets you feel you need to rest for a minute or two and maybe catch your breath, go ahead. If you don't, and you feel you can just immediately go on, then do so.
Hey faz, just been busy. But now I'm scaling down work, so working out and HST got back higher up in the priority scale.
Been online for about a week already, I'm seeing a distinct lack of the old-timers. You're about the first person I've seen here again from ye olde times.