If the servers did crash it wouldn't take 6-7 hours, would it?
No really it varies there is no way to tell a exact time they will be back up for now it may be good to play a map the new one on the home page is pretty fun but hard on easy so its a great challenge.
I'm not a technician or anything but I think it could take 6 hours to fix a crash.
http://www.minecraftforum.net/topic/1586068-mojang-server-status-session-servers-are-offline/