In my expirience the patch does not last all day. And I'm usually at work when they start patching, so i don't have to wait several hours to get online when the game is patched. However, some RL stuff do take all day.
This patch is kinda huge with the BS fixes + DB3 etc. DB3 is especialy cool IMO, and it would be fun to try it out before someone has figured it out, and tells you the trick on how to do it.
There you go. My reasoning for making plans to play AO for half a day.
EDIT: :O 1h(ish) down time! Im not even home from work yet i guess i dont have to wait at all then.