Try just a basic timer with 1/2 hour increments. They're the least expensive, and for foggers, you don't really need more precise timing. Often, it is vastly over estimated how wet the fogger will really make your cage. In most situations, you'll find a fine layer of moisture (similar to dew drops) all over the surfaces of the cage, but rarely does the substrate become wet enough to cause problems. If 1/2 hour creates too much moisture, just dial down how much comes out when it turns on. ZooMed foggers come with a dial that you can use to adjust the amount of fog coming out. Theoretically, you could run the fogger all day, just on a lower setting, and have the same effect on humidity.

However, running a fogger for 1/2 hour, 3 times a day, should work well for your ball python. I run a couple at home for 1 - 2 hours daily (often more!) for my amazon tree boas and vivarium tanks, and still find that the substrate has plenty of time to remain dry.

-Jen