Well, most contacts will say on the bottle/box how long they can last/be stored.
However, I know for a fact that the 3month use ones *can* be used up to 5, but it depends on a number of factors, such as how dry your eyes are, how quickly gunk builds up, how well you clean/soak the lenses between use.
It also depends on your eyes in general, personally, I wear long-term contacts all the time, and have very..strong eyes. They're weeklies, but I can wear them up to a month before they need changing. Colour contacts, even larger ones I can easily sleep in with no problems, and have never felt any real change until around the 4-5month mark.
A few of my friends work in optometry, and according to them, if you have allergies, or suffer from dry eye, you probably shouldn't use them much past the recommended date. At that time the contacts will be less pliable from use, and might be uncomfortable for you. My eyes are naturally pretty watery, so I'm more likely to actually have my contacts slip right out (or behind my eye, which has happened once now).
I would stick to what the packaging says, but by all means talk to your optometrist and see what they say as well.