"After a 4L of ice cream and surfing the internet, she often concludes her activities with a nightcap and succumbs to laptime."
Laptime has a greater occurrence for those that stay up late, were partying last night, or those who ditched work in the morning to ski fresh powder.
Used by those that know the falling asleep on the keyboard can be hazardous to one's health due to short circuiting, and also to one's employment should the boss happen to saunter by.
Cal: Its laptime for him, again... He must have been out all night!!!
Usually happens when watching a movie or somesuch and the relationship is comfortable/intimate enough to allow for the tired one to fall asleep in the other person's lap.