i wear monthlies normally, and my optician said 8hrs a day tops, but i wear then a lot more than that and don't have any problems apart from the occasional tiredness in the eye, i've never got anything for it, but i think eyedrops can help
when i went to a festival though i effectively used my monthlies as dailies because i was due to change packets anyway.. and just used an extra packet (so got through 3 months worth in 3 days) but wore them like 16++ hours a day.
it's easy enough just to chuck them out when u go to sleep, and if you're too drunk to remember then it's no real big deal if u sleep in them, you might jsut get a bit confused and think "I'm cured!" when u can see in the morning lol.