That's seems like too much. Since you have figured out how long it takes you to apply half inch, then just watch you lawn. Count how many days before it starts to turn like an ash green. That's when you need to replishish. Next time try to apply it the day before it will turn colors (based on your previous count) There are other methods (moisture probe), but this visual way works pretty good for smaller lots.
PS - could you update your profile with your lawn size? It makes it easier to give proper recommendations.
PS - could you update your profile with your lawn size? It makes it easier to give proper recommendations.
