In general a creature should not be left on a leash for any long period of time typically no longer than 5-10m at a time.
Longer periods are not only a waste of time they can cause some really bad effects. The leashes are training aids not a substitute for training.
Hmm it weir I think.
When I played BW1 my creature was acting very weird.
He picked a cow and then gave it to big creature(Guide,ex creature of nemesis)