Been a few years since I was on the Sun Dancer 2 (since renamed Belize Aggressor IV); have been on Cayman Aggressor IV and Turks & Caicos Aggressor II. IIRC, the pattern on the Belize trip, and it seemed to be fairly common, goes something like this:
1.) A guide leads a group dive. You and a buddy are free to dive as an independent buddy pair if you wish.
2.) Guide brings the group back to the boat roughly around 45 minutes or so. If you want to mill around, sit on the 15 foot hang bar and look around while running up your bottom time, etc..., you can.
The guide has to plan around getting back to the boat with the highest gas consumption diver not running out of gas, and most divers are diving 80-cf AL tanks. I doubt anyone's going to kick your friend out of the ocean at the 40 minute mark, but if using the guide, the main 'reef roam' might last close to that. But there are things to see near the boat, or while at the hang bar. Note: The Belize Aggressor III and IV look considerably different.
Anyone else been more recently and recall a different experience?