How long you may spend outside of the space station for spacewalk?

I know that what I’m going to ask is only out of curiosity since I will surely not have the opportunity to try it in practice, but I’d like to know long one may spend outside the space station for a walk. The space has always been fascinating and a bit frightening to me and I can’t imagine myself taking a walk on some distant planet.

Well, I guess that it depends on how much oxygen one has in those storage tubes, but I reckon that it is not recommendable to be outside for more than 2 hours. I also don’t know what kind of impact can the fact that the planet, on whose surface one is walking doesn’t have gravity, can have on the body. I also have a certain fear of the space and that is the fear of the unknown territory and the possible danger. Besides I reckon that it is very calm and quiet above which is really making me feel nervous. I admire the people who had the courage to travel to space and do researches though they didn’t know what they could encounter.