I have been experimenting with cutting the time in half. Do 10 minutes, jelq, then do 10 minutes more. Then adjust it as you go along. They recommend no more than 20 minutes. For me, it depends on how much pressure I'm using on the [words=https://officialhydromaxpump.com/?uid=6&oid=2&affid=98 ]Bathmate[/words]. One 20 minutes session I pumped that thing till I couldn't squeeze out even an air bubble - my dick expanded 1" in girth. It was freaky. But I haven't gone that much since then. I've gone with lower pressure for well over 30 minutes to an hour without any unusual problems. I find with the lower pressure and longer time I get less fluid build up and a good expansion. I usually go to about a medium pump pressure..sometimes I'll pump it up as high as I can for about 5 minutes then let the pressure off and pump back up to a level a little lower than max. Sometimes I'll do 5 minutes, then let the pressure off for a few minutes, then 5 minutes, etc...
The point is to experiment to find what works for you. IMO starting lighter and working up from there is better and safer. After my 1" expansion session I knew internaly that it wasn't a good thing for me to do....so I heeded my intuition and haven't done it since. The day may come when I do it again, but that won't be until I've conditioned myself to be at that level.
Have fun with it...