To really be proactive in eradicating mites, you need to treat for at least 45 days, if not 60. Some keepers treat for 90 days to ensure all mites are gone. A snake mite's life cycle is approximately 30 days, so if you just treat for a couple of days and stop, you aren't killing any new mites that are hatching out in the mean time & reinfesting your snakes. Mites can travel very quickly - up to 50 feet in an hour, so this is the "space" you need to think in terms of when treating them. Using a spray for treating the cage & surroundings works well. You should also vacuum the room thoroughly to get any wanderers. Wash hides & water bowls in a solution of hot water (110 degrees+) & bleach, to a 10% dilution. Mites are not a "treat once or twice & you're done" sort of thing - you really, really have to stay on top of them if you're going to get rid of them all.
Good luck!