Their website doesn't have specific Christmas service hours or information. I've read somewhere that the service begins at 11:00 AM. If this is true, how long does it last? We have Eiffel Tower reservations at 1:30 PM so we want to be in the security line by 1:00 PM at the latest. Worst case we'll sit towards the back and sneak out when we need to.
Was just in Paris in Nov so signed up for lots of sites. Just got an email from St, Sulpice re Christmas schedule.
https://www.paroissesaintsulpice.paris/vivre-lavent-et-noel-2023/
Enjoy.