My CPU fan is threatening to give out - How much time?

[James]

Long story short; Thursday night, computer starts making a soft buzzing noise. Further inspection reveals the source is most likely my CPU fan. If this is an indication that the fan is on its last legs, what exactly should I do while I wait for the chance to get it replaced?

I turned my computer off when I wasn't using it. However, when I turned it back on hours later, the fan made a godawful noise, and I turned it back off. I turned it on again a few moments later, and that noise is gone, but the buzzing remains. So I'm worried about that. But I'm also worried that running my computer 24 hours a day will cause a problem as well. I also don't think I'll have a chance to take my computer anywhere until Thursday.