James,
I just stumbled onto your post while working on updating a heavily hacked version of the Face to Face module we are using. I have included this ability (to shut down cancellation a set time before the lesson). Right now it is hard coded to 24 hours prior to start time but my intention is to make it an adjustable setting via the plugin interface.
Actually, I've just completed some long overdue work on our modified version making it slightly more viable as a community offering. We are using it on 3.3 but it should work on versions thereafter. As Dan noted in a message on the plugin page for the version available here on Moodle.org, the version I have is not compatible with the 3.6 privacy api class functions...and I'm not sure if I'm capable of making those upgrades...
At any rate, if you are interested in giving our heavily modified version a run, feel free to send me a personal message via the forums. I can send it your way as an e-mail attachment.
Regards
Jason
P.S. For details of all the features our hacked version offers, please refer to this forum post: