Gary is correct, however, that depends on the muzzle brake you are going to use, Vais, Quiet, and other radial muzzle brakes (port holes all around) does not require indexing, thus can be installed onto the barrel without receiver installation first.
Not my muzzle brake preference but an option, there are many happy end users out there though.
Anyways, going back to your original question, the best time to install muzzle brake is to have it done ready for you to enjoy when you get home safely.
Watch your six and thanks again for your service to our great nation. Cheers!
I voted for my "FREEDOM", "GUNS", and "MONEY" - keep the change - UNK.
"I am always proud of my country!"
"Leadership Rule #2: Don't be an ***hole." - Maj Gen Burton Field.