i also dissagree with the time limit, whats the point? whoes it hurting? why does it matter how long anything takes?
what if you decide to completely change plans, classes (if possible... we dont know this yet) things like that can take time.

also, what if a party member DC's or just leaves the group, i hope there is a system of re inviting or replacing that person. this is another thing that can take time.
so why the 60 mins?
they must be very small dungeons.