Wait? Don't wait?
You can make the pos space booking, select your seat on united.com and then hold off getting it authorized (up to 72 hours) . That way you can get a seat tied up but not commit to deviating until the last minute.
Also, when getting crew desk to approve your deviation, have them authorize your booking during the same call.
The front end dh AND back end dh can be in the same booking.