The problem with that is that external meetings will still start on the :00/:30 so your overlaps will be a problem or you'll lost another 5 minutes from your in

The problem with that is that external meetings will still start on the :00/:30 so your overlaps will be a problem or you'll lost another 5 minutes from your internal meetings when anybody on the call bumps against a :00. Besides if you start all of your meetings at :05 as a company you'll still have people wandering in at :07.