How come that sometimes i can have sex for 1 hour without coming, but other times i feel challenged to survive 2min? (male-20)

Two minute mile: Set, setting and substance. If your mine set is oriented to a destination that is where you will most likely end up. Is it concern about both your and your partner's satisfaction? Is it to rush through fearful you might lose your erection? Is the setting one in which there has been considerable conversation and foreplay? Do you discuss your expectations about sex with one another? Any alcohol?

Many variables : That can vary with the time of day, how rested you are, use of medications or alcohol, as well as the nature of your relationship with your partner.