When do you add the file powder to gumbo?

file powder is usually added at the last minute before serving or left to be added separately by person in their bowl.... if file powder is added to early into your gumbo it may become "stringy" and lets say separate in a way.... extra tip when adding roux to stock make sure one of them is warm while the other is in room temp and mix lil by lil..... so it wont clump...... chefboimanny