i would start them up with a new tank cause it takes like a month to cycle and a month for the bio pellets to work so u will just have a clean tank that never gets much algae.
those bacteria might also keep u from seeing any real ammonia/nitrite spikes it couldnt hurt.
The best time to start is BEFORE you have a NO3, PO4 problem. Often people who complain about biopellets is because they added them to a tank with NO3 and PO4 existing and they stripped the tank of these nutrients too fast.