Your critters are usually what need O2 at night. It's fine to leave it running 24/7. Just increase surface agitation of your water at night or use an airstone if you're concerned about things or see your fish gasping.
While it can be done (and I've done it a couple times), it's not really cost effective (when you consider paintball setups are cheap) to add a method of evening control. Typically involves creating a reservoir bottle with a manifold, safety release valve, ball valve and such.