Indeed - as per any on >>>>>
http://www.networkrail.co.uk/aspx/3828.aspx
Not that very much is about to change, as far as I can see.
But I confess I had assumed it was Monday.
Is this a new(ish) thing? I thought in ye olde days (I mean BR era) that the timetables changed on a Monday. (of course, the dates used to be different - used to change in September, not December.)