Yes, exactly. Keep 'em busy. Easier on the body. I'd change it up as many times as possible in that 5 minute block as well. I might go so far as to suggest the first group "perform" dead centre in that 5 minutes before clearing the stage for group two to join and so on.
From a visual standpoiint bringing in four groups of 25 will never look as smooth as rows going up because it will be more building block into corners. Combat that with using as much sky space as possible with each group going up with corners "shrinking" in as the sky becomes full. IE, group one performs as required. When group two is ready to launch group one forms up their quad in a top grid position wiating on group two to form their grid. At that point they perform as 25 in whatever logical fashion is dreamt up until group three is ready. Etc. Hard to properly put into writing what I'm getting at. Hope it makes some sense!