By 8 pm the Europe rush should have cleared, so wait shou;dn't be too long. I'd guess no more than 15 minutes or so.
But of course depends on staffing etc.
Hint -- you're presumably on United. When they put you on the mobile lounge don't go to the back, even though they will try to get you to. If its fairly empty, squeeze into the little space in the middle behind the driver. About four people can fit in there
First off = first in line.