I suffer from your DH's mindset and constantly estimate short - there's a mysterious 10 minutes in there somewhere that occurs sometime after I think "time to go" and pick up my handbag and when I'm actually in the car driving up the road.

Doesn't help that we live muuuuuch further out than all our friends and family and so constantly have to leave eons before anyone else to arrive at the same time. The only way I can make it work is by guestimating how long it will take and then adding 15 minutes, and then I'm usually about right.