You'd better wear contacts within the days as your doctor recommended you to. More and more deposits will be built up on the contact lenses more frequent / the longer you wear your contact lenses, which will block the transmission of oxygen. As we know, Oxygen transmission is critical for your cornea's health!!!! Lack of oxygen of your cornea can result in damage and problems like a corneal ulcer, corneal infiltrate, infection, corneal neovascularization, corneal edema and GPC.
That depends.If they are daily disposable contacts, you should wear them for one day and throw them away in the evening and open a new pair next morning. If they are weekly disposable contacts, the lenses can be worn for 1-2 weeks, but you should take them out and place them in contact lens solution when you sleep.
It is highly recommended that you should not wear contacts for more than 8 hours per day no matter what kind of contacts they are. If you leave them for more than a few days,your eyes can get infected easily and even ruin your sight.