Yes. I don't recall the exact numbers, but it's something like 12" for conduit and 18" for direct-bury cable.
As for gluing PVC pipe, the best tip I ever learned from someone was to prime, glue quickly, then push the fitting on, and twist it back and forth until it locks up. That helps keep the glue distributed, and it prevents the hydraulic pressure of the glue from pushing the joint apart before it sets. It seems to speed up the set, too.