YMMV but IME it’s generally been on time. Headed down at 10:15pm last night and F/J boarding began as soon as I got there.
Also with the extension of the A pier of T4 it’s not as much of a mess as it used to be, more space for Y pax to line up on the other side.
Plus I like boarding early
I like boarding early too but not if I have to deal with a mess at the gate. There are so many C pax on this flight and not a separate line for F that it’s usually just better — for me — to wait in the lounge.