You're doing it wrong
Perhaps a slightly unfair title, but still..
There are plenty of apps that manage alerts and stuff far better. I, for instance, use Locale.
After 11pm at night, if my phone is plugged in to the mains, all alert noises are switched off and the phone turns to silent non-vibrate, except for alarms. Come 7:30 in the morning this is all enabled again, and because all the alerts came in on silent I don't get a suddeny cacaphony of bells, whistles and shrills that would cause me to destroy my phone in slumber-induced rage each morning.
Even more helpfully, when I'm at work my phone knows and turns back on it's STFU mode, so I don't make my 3 colleagues mugs of tea look like something out of jurrassic park every 5 minutes.