Thanks.En Banc means that it will be heard by all 4th circuit judges. Really there's no time frame. Probably months - maybe a year - maybe longer.
I have stopped believing that court is anything to do with justice - it has more to do with theater and advancing their political ideals. There is no doubt in my mind that they will push this as long as they can. If they can they will wait for the SCOTUS makeup to change so they can decide how they want and not be at risk of being overturned.
Doing a little googling, 4th CC has 15 judges, as of July this year 14 with one vacancy. 8 of them appointed by Clinton, Obama and Biden, 3 by Trump, 1 by Reagan, 2 by Bush.
I also found a list of en banc cases showing dates of the appeal and time frame for decisions. Yes, most were months maybe a year or longer.