Funnily enough I'm looking at this very thing myself which is how I've ended up at this thread. One of the issues we hit was that the Meru support for 'public' devices is pretty poor, no link to AD, no transparent proxying. We're going to get around most of the issues by using a Smoothwall firewall which does both and will also act as a DHCP server.
I'm not sure about using Meru on a VLAN, do I need to set up the VLAN on all intermediate switches ? I know you normally would, just wondering how the APs talk to the controller.
As far as timing goes, I'm not sure that can be done with what you seem to have available. You *could* set up a daily guest user, that's a drag but I can't see any other timings available on Meru.