It doesn't take two hours.  Maybe the temp. crown just doesn't have
great retention.  If it's made of acrylic, sometimes the retention can
be improved if it's relined.  If the tooth is too short, sometimes it's
tough to get a temp. crown to stay in.  If this is the case, the dentist
needs to evaluate whether there will be a similar problem with the
permanent crown.
Saying more would be just speculation.

Steve