It has been saying that for many months now. The w/c is just the current week date... carp Freeview way of presenting info as they really need someone to interpret the Arqiva Planned Work Messages (assuming they even see them).However, the maintenance notice on https://ukfree.tv/transmitters/tv/Sandy_Heath has now changed to say "week commencing 27/11/2023", so I guess whatever they are doing isn't finished just yet.
I note there are an awful lot of major transmitter sites with the same work going on... including Crystal Palace and Rowridge (again). That seems most improbable as Arqiva won't have that many staff (or contractors) trained to work on the components that will give those sorts of effects when switching happens.
BBC Distribution will negotiate with Arqiva over some of the more likely to be obvious to the viewer works wrt times for switching (which should only be brief).
Fringe area reception issues are possible if working on reserve antenna (with switch to/from main at start/finish of works). I'm not fringe. That would still be indicative of a sub-ideal receive antenna installation in many cases.