How long does the screen's device context handle last?

Say I use GetDC(0) to get an hDC directly to the screen, how long before that number is no longer valid, and I need to get a new hDC for the screen? Does this happen each time the screen is refreshed? Or does the screen's hDC last indefinitely. I vaguely remember reading documentation somewhere that an hDC shouldn't be stored, because hDCs can change, so you should get an hDC right before you need to use it, rather than storing it and using it later.