I just restarted them. So far I'm up to 60 sec X 2. They're good exercise, I've found in the past.

I do them about 15 minutes before the rest of my workout. that way, I have full strength to devote to them, but plenty of time to rest up before I do the rest of my exercises.

BTW I hate them!!!!! The most boring of all exercises, and they make me feel funny. But I know they work, so I do them. (usually )