I dont know where you got the over 55 minutes is to much thing but i dont think its very valid.
At the gym i go to our workout are 2 hrs minimum. On fridays its 1hr straight cardio circuit training. Then we have a 5 minute break and either roll or spar for another 30 mins to and hr.
A good rule is to just listen to your body. Some people can train more then others for lots of differnt reasons.