As do I, but the OP is BIAB so his best bet is most likely to add them immediately after pulling the bag and right before he starts the flame on the boil kettle.
In BIAB, I always aim to get some soak time for FWH prior to ramping up to the boil since that better approximates the “traditional” method of FWHing. I’ll put the hops in alongside the grain bag and submerged. I generally do this as the mashout begins. This gives the mashout time plus ramp-to-boil time for the FWHs. That’s how my drummer beats
I do first wort hopping quite often when I do BIAB (full volume). I have always added the hops right after pulling the bag. Heat on the stove goes on and the hops go in.
For FWH I slip the hops in as soon as I raise the basket high enough to get clearance, then let them steep for about 30 minutes before cranking up the power to start the boil…
FWH is no more special than boil hops. Add them anytime before reaching a boil, or even a minute or two after. You shouldn’t be able to taste any difference.
Do you find that this is hop variety dependent? I’m mainly curious about it if someone was using some really punchy hops (CTZ maybe) but wanted the bittering intensity/harshness to be lower while maintaining the flavor aspects of that hop.