Since every one is different, the best is dont think about it. it could be as short as 12 hours..or even 6 for some (?).

why worry about something that you arent sure yet. because no matter how much you think ahead and try to prepare yourself mentally, when labour pain kicks in, everything goes out the window.

get ready things necessary in a bag, and just wait.

for my wife though, it lasted around 10 hours..by by the 8th hour, epidural was injected so she claimed she's not in that much pain after that.