You need to know the soil type you have. Sandy Loam is COMPLETELY different than Clay, and it is not dependent on how far the screwdriver will go in. I have nice, solid Clay, and the screwdriver will go in pretty easily when wet, and almost not at all when dry. Clay holds a lot more moisture than Sand (although that doesn’t really make sense to me, it’s true).
If you’re certain that 30 minutes is the right amount of water to apply, then fine, but changing nozzle inches per hour without knowing what it actually is, or deviating from recommended values without knowing better, isn’t a great idea. It’s best to be sure of this value, either by spray head specifications or measurement.