I have several pistols in my 65 that were hitchhikers on my TBS rock. One was paired with a sponge! I THINK I have 3, and they've each moved several times, except the sponge guy who sticks solely with is sponge.
I have a pistol/goby combo in a nano that went in together, and that pistol went to work immediately, and was immediately LOUD.
Wait and see attitude. If you have some, spend some time sitting by the tank watching for puffs of sand... sure sign of excavation. Or, if you notice general cloudiness at some point...yep! burrow work is happening!
Good luck, and I hope you see your pair soon, they're a lot of fun to have and to watch.
But, plan on re-stocking snail and crabs fairly often!