Of course, you're limited by the size of your SDHC card, but on the MP4 video setting, you have 29 minutes, 59 seconds you can record non-stop. You are also limited as to using no more than 4 GB of space on any SD card. As far as HOURS non-stop, you can't record that long, and I haven't seen a camera yet that will record for hours at a time non-stop. Your battery would drain before anything. As far as low light, the flash doesn't work during a video, but if there is some outdoor lighting, it's decent.
I got a 32 gig memory card and aftermarket batteries, that were higher capacity. I hit the street in Vegas and shot all of the video, stills, panoramas, flash shots etc and had did not run out of battery power or memory space. It would run longer on one battery than I wanted to be on my feet. It appears to not be a watt hog. Transferring large files out of the camera is a different story. Better to take the card out and not use the camera for transfers. I have not conducted the test of putting it on the tripod and letting it go. If you want to surveil, and see what the GF does when you are at work, I think external power is what you need.
I do not recall the correct term for the setting that equivalent of film speed. This camera can be manually set up to at least ASA3200. It appears to be fairly good at the low light settings; I can shoot in dim room light and get a usable image without too much noise. It is ok to document something with that setting- not for award winning photography.