My longest maturbation was 2-3 hours. But it happened only a few times with my brother. We really enjoyed jerking together(everyone with his own tool!) for very long time when we lived together. We watched porn,used tons of lube to jerk better,changed different porn movies and many positions. We also used sex toys;mainly fake holes to DP with our thick cocks....great time we had!
Of course we stopped for a few moments or slowed the speed down a bit before cuming,so that we could last and last... After two hours I assure you that we came sooo much, minimum 7-8 long shots.... but normally I jerk off between 1 minute and half an hour,depending on the time I have,how horny I am and if I am looking at porn or not....
It is normal for a man to be able to cum in one minute or less,but masturbating for a longer time is a good way to train yourself to last more when you have sex!;-)