December - totally wrong month. Attendance would be miniscule. Also government have been told by banks that most people will have been notified by end Dec.
Wednesday 10th/17th January far better dates. Competing with very little, so max publicity, end Dec deadline for banks will have passed, so there'll be a valid reason for protest.
Dec 8th is a Fri - worst day of the week for a protest, Christmas (and the stress of it) a couple of weeks away. Banks could simply say "we're working towards the agreed timeline" Turnout would be tiny.
Plan it for 17th Jan. They'll be plenty of noise after the end year deadline. If banks meet deadline, call it off. Likely they'll miss, thus national publicity and press will.get behind the protest - mid jan is nearly as bad as August for stories to fill pages and press wil jump on anything