I've never timed my orgasms, but I would guess that they only last mere seconds. However the buildup to an orgasm can last quite some time depending on my state of arousal which are dependant on my partner's actions, my physical attraction to my partner, whether or not I'm tired, how many times I've already orgasmed, etc. I always feel my orgasm building in my toes and then working its way up my legs and into my midriff before finally bursting out of my cock.
If I'm just jerking off I my orgasm still lasts only mere seconds, but I can either prolong the buildup, go for a quick ejaculation, or somewhere in between.