This is starting to sound like "Nobody goes there -- it's too crowded."
Kinda surprised no one's mentioned that their Web site has useful information. Of course, they're hip and stylish so it's a JPEG and not text, but here it is; note the General Info and Hours sections:
So the kitchen is open when they're open, which is 3:30 p.m. every day of the week. And they seat in the order of party arrival and completion, which means there is an advantage to the first person in the group being early and the last person in the group being prompt.
Avec has many (10 or so) communal tables that seat 8 as well as bar seating. The larger our group, the trickier the wait for a table, though in my experience if they know a group is coming, they will try to accommodate by filling gaps at other tables. While they don't take reservations, they aren't jerks about it either.
I can do 6:30 or, really, any time that day.