I've had 1hr doubles before and for me it was exhausting! Because when you are doing double, it's 100% full attention on you from 2 girls, which makes is 200%. I now switch to half hour, which is enough for you to climax. I mean at the end of the day, it's about you, not them. Also that way, you can try another pair of double girls without waiting for more $$$ to come into the bank.