Good to see some ideas being generated about parking in the area.
Personally I would save make parking free for up to 3 or 4 hours. Plenty of time to do relaxed shopping and not having to chase the clock, but time to go to more shops etc as opposed to nipping in for an hour and just the one place.
I don't think it should be free all day as then the places could be taken up with workers, although I think that should be another issue to be dealt with so there are plenty of places just outside of town and not have too many residential restrictions. No point in making town centre parking free, for them all to be taken up by workers' cars and none left for shoppers to use.