I change my infusion sets every 3 days, but if I notice a sudden high pattern and I know there’s no possibility of a problem (bubbles) with the cartridge AND there’s nothing else that could be causing the high, I know it is the infusion set causing a problem and I change it early. Also, change it early if it hurts or if you can see that is looks bad.
As for the cartridge…I use them completely or nearly completely–until they are empty or almost empty of insulin. If I know I will have easy access to a bottle of insulin and the new cartridge, I will let it completly run out. But, if I have somewhere to go and I know that my insulin would run out (I look at my basal rates and make a rough calculation), then I change it before it fully runs out. I hate the idea of wasting insulin, so I try not to.