I've used the Unicolor kit, and the Rollei Digibase kit (in addition to the straight Kodak Flexicolor chems) and neither mandates any extra times for reuse. However, I've heard of people saying that their kits did in fact call for it, so like wblynch above I add 15 seconds or so after a few rolls if I think the chems might be getting tired and could use a little boost. No more than a few seconds, though, else you'd be effectively pushing the film.