I think the shortest campaign i ever played was approx 16 hours, uesugi/expert/huge units/v1.12. I finished in 1548 and about 4 hours were the sieges. I played all battles and didn't use the speed slider. i played them straight - it was a great camp.

Usually i dont get that lucky of course and campaigns last far longer (for days with brakes), especially when choosing southwestern clans like the Mori and the Shimazu or the Oda. I haven't played the Hojo in a long while; they are the easiest imo and for the same reason good for beginners; it was the first clan with which i managed to succeed slightly with (like holding my own and not getting wiped out) 10 years ago when i first played.