
I don't see the issue as being undoable:
you can program how _long_ someone has access already, the exact times would be additional fields.
There would have to be a setting for local access point time which was corrected to DST or so..
Then the radius server would always know for a given stationary AP,
what time it was at the AP. The WorldSpot interface for these local hotspots around me always seems to be off by an hour but this hasn't been an issue. It would be in the case of managing bandwidth, changing the parameters during the day.
Maybe another issue is once the session is started, there is no way for the radius/web servers at worldspot, to intercede to the AP's chilli software, sending the command to reduce the client speed? There is a way to cut the client off, and there is a way to set the speed initially, however flow during usage is controlled actively at the AP client.
Just some ideas...