I'd second the "don't worry about it" mentality. No real scientific data to back me up, just observations that few troops use hearing protection. Like someone said though, if you have time to get on earmuffs, you have time to do something else (911, evacuate, lock the door, etc).

I'd worry more about the gun "exploding" when you shoot for the first time at night. If you've never done it, you'll be seeing lots of gasses venting that you don't see in normal day light shooting. Be prepared for that.