i like the idea on a 3 day event but not 7 minute heats. you can still get 4 heats of 10 minutes in quite easily cutting down the 5 minute warm up.
in the case of this years vics i think it would be wiser to just finish up early enough on the sunday so people have enough time to travel home on the sunday. if racing and presentations were finished by 1 or 2pm most of the VIC and SA entries would be home by 8pm