I was about 19 years old and I have not gone back to diving about 12 years ago, if I remember well we were only about 3 or 4 minutes at that depth, we did not use any special mixture, we made stops one at 15 meters around 50 fts from around 6 min and another one 5 meters around 15 fts 3 or 4 min, we made another about 2 meters but that I don't remember well how much was maybe the instructor was ultraconservative.

I still have the tables to calculate those things.