It depends on the type of red contacts you are buying.
If you are buying theatrical red contact lenses then they are typically not designed to be worn for long periods.
Usually the manufacturer will recommend that you wear them no longer than a few hours, long enough to wear your costume to a party, or go trick or treating.
If you buy red contacts that are prescription and designed for long wear, usually tints, then you might be able to wear them for long periods, and even overnight. Colored contacts with unnatural colors are typically going to be costume contacts though, so this is usually not the case.
If you plan on wearing them longer, consult with the manufacturer and possibly your doctor or eye care specialist as well so they can verify that this will not be a problem.
After you wear the red contacts you should always let your eyes rest, store the contacts properly and clean them before you wear them again.
If you have several occasions in the same day to wear them, if they are not designed for long wear, you should give a couple hours between each occasion for safety.