Seems to be both Wednesday and Friday. I was there last night (Wednesday 8/19) and there were about 8 people playing X-Wing. I was also there 2 Friday's ago and there were a good 14 or so playing that night.
Wednesdays is open-play for X-Wing, and Fridays is the DLair X-Wing league night. Echoing craigmray4, there are usually more people on Fridays than Wednesdays.
I think the guy running the league there is just a fan not an employee, probably why the discrepancies. And don't believe he is on this forum, but he does post on ghe ffg forum.
And i do know some folks who show there on Wednesdays but not regularly
The Wednesday event is just a casual thing that includes X-Wing, Armada, Firestorm and anything really that includes spaceships and minis. There are some players that want to play on that day but do not receive official support.
I am the X-Wing organizer for the Friday league (my posts keep getting moderated) and that hasn't changed since January. I am not an employee but I work closely with the store for all events. I receive the official FFG prize kits and have first dibs on X-Wing tournaments.
I encourage players to attend Fridays as we have gathered quite a few players weekly now.