I believe the first one should be changed after a few thousand miles, the second a little longer, etc, until you get the initial "gunk" out of the engine. Then just make it a regular change. You'll be able to feel the return hose while the engine is running, if it's cold then the filter's clogged and needs changing. Here's
one such system with some pics of what you'll get out.
08 6.7 QC SB 4x4 "hand-shaker" edition, De-Badged, EGR Delete, TTT Mirrors, Auto Exhaust Brake, etc.
All details and instructions --> www.CarboniteCummins.com
Successfully blew up three 6.0s before moving up in the food chain.