Timetables are being prepared and are nearly complete.
If you will be going by train to Charlton on Boxing Day, an hourly service will run starting at 0651 to Three Bridges, only calling at Haywards Heath. This will connect with a bus to East Grinstead (takes 20 minutes) which will then connect...
Depends who is doing the work.
I'll bet on a 2 day overrun with the junction and signalling at Victoria, and a 1 month overrun on the new platform at Gatwick.
29th ? No. Either a long-winded diverted service would run up to London, or it's a bus from Three Bridges to East Grinstead to pick up...
Work has gotta be done, anyone can tell you that the junction being replaced (Sloats Nest) is incredibly rough to go over. Signalling faults are common at Victoria to the new system should sort the problems out and the new Gatwick platform should ease congestion.
No other time to do the work...