Depends on what time I have to work the next day. I build my entire 'life schedule' around my work schedule. I try to get at least seven hours of sleep on average. I usually set my alarm to allow for an hour of leeway time to get ready for work--thirty minutes to get ready and another 30 for heading out and catching the bus, which runs on the hour (though overall it slightly varies). So to put it in simple terms, if I work a 7am to 3:30pm shift the next day, I set my alarm for 6am. If the bus comes at, like, 6:30, however, I'll set my alarm to go off at 5:30, as that allows for an entire hour to get ready and eat or whatever else before heading out to the bus. (The bus ride itself takes fifteen minutes if things go as planned.) I hate being rushed. The same principle applies in the rare event that I actually have plans aside from work, such as heading out to the blue mailbox and mailing out the rent before pick up time.
I tend to go to bed whenever if I have the next day off.