How long is it safe to leave my contacts in?

Overwearing contacts restricts teh flow of oxgyen to your eye and that is dangerous. You don't get warning signs like irritiation , in fact your lenses can get more comfortable. Red eyes when you take them out is a danger sign So how long is too long? Well that depends on the brand , you etc. but broadly I've seen optiicans post that 15 hours a day is fine. Its a good idea to let your eyes be free at teh beginning and end of the day and if you can the odd day a week totally free. Checkups pick up oxygen deprivation as well as other things so dont' skimp on checkups.

Yes - vision with contacts is better than with glasses. Just be careful adn stick to the rules.

They say 24 hours but I always just went until they started irritating my eyes...

I'd say 8 hours maybe but keep some saline solution with you