Originally Posted by rubiksoval

It's generally accepted that vo2 max isn't even reached until at least 2.5 mins into an effort, thus intervals should be a minimum of that to elicit the most amount of time possible at vo2max.

Just going 30s-3min at a time is going to leave so much down time that you're only going to be reaching vo2 max at the very end of each interval, and not maximizing the amount of time spent there.

But whatever works for you. Many ways to skin the cat. I like bang for the buck myself, though.