me and the girlferiend are having a lil dispute about how long u can leave a laptop on for, iam converting something on her laptop and its gonna take 18 hours to complete, so i wanna leave it on overnight or until its finished anyway. She reckons that they should'nt be left on for that long because they get too hot!.

So question is, is it SAFE to leave it on for a good few hours maybe a couple of days if need be, or,are they not made to be on that long?