I'd have about 2 hours on my laptop battery and since my router is plugged into a UPS I could probably be online for the entire time so long as my desktop computer wasn't turned on.
I lost power once for an entire day. This was a few years ago though, something happened to one of those power boxes (all our power lines are underground). Just our street was affected. It sucked for me because I was stuck inside anyway due to an injury from the day before (took a surfboard in the mouth, split my lip wide open). I had stitches and my bottom lip was all swollen, I looked like hell for a couple days.