Well, in my experience as an openly gay man, more often than not, there was "after-play," expression of gentle natural affection after the actual act of sexual intercourse. If in bed, we did not go right to sleep unless we had been tired before we went to bed.
In the book, it could have been 3:00 a.m. or later in the early morning before the guys went to sleep. Since after 2, Ennis was "dizzy drunk" before he slept for a while (Ennis did snore) and then woke up Jack with his teeth chattering, I prefer to think that the deepened intimacy was longer than the sex act and because the both of them were really tired, they quickly went back to sleep as soon as Ennis withdrew.
But, there are some guys who do not like to be touched at all after they have sex because the nerves in their skin (all over) become too sensitive.