1"+ of water a week is true, but that’s an average value. You’ll find you need about 3 times the water in summer than you do in winter (well, maybe Las Vegas will be closer, with warmer winters). I’m guessing you’ll need over 1.5" in the summer.
You can determine how much water you need per week using the National Weather Service. Go to that page, then the second dropdown, go all the way to the bottom to Total Weekly FRET (in). For the Las Vegas area today, it’s about 1.9" per week. Now, multiply that value by your crop’s/grass’s Crop Coefficient (mine is 0.85 for Centipede grass. I’ve seen recommendations for Bermudagrass from 0.7 to 0.85). Let’s use 0.75 for an example.
So you’d want to apply 1.9 x 0.75 = 1.42" of water this week. That will be far less in the winter, and will do doubt get higher in summer.
Applying the total of 1-1.5" of water in one watering may be difficult. Most soil cannot accept that much water at one time, plus going a week may be too long, depending on the heat.
With my old watering system (not Rachio) I adjusted the system to provide 0.85" of water (1" x my Kc of 0.85) with a 100% Budget setting. Then, each week, I’d go to the above site, and change the Budget to match the value on the web site for that week for my area.
Now that I use Rachio, Flex Daily schedule, and I let it do the work instead. It calculates the Crop Evapotranspiration each day for each zone (the FRET daily value x Kc). So it totals and keeps track of the water added, and the water used, and determines when and how often to water.
It sounds like you’ve calculated how long sprinklers need to run, so by doing that, you can get the Nozzle Inches per hour for each zone. Setting that, in addition to other settings for your soil and crop, should set the system pretty accurately.
