Question
we bought an house that has a auto sprinkling system and we live in Indiana. what is the best time to set this unit to come on and for how long running when it's in July and August
                    thank you
                        don

Answer
Hello, Don - congratulations on your new home.  I will try and answer in generalities, as the information you gave is pretty broad - such as how big an area to irrigate, the types of plants (shrubs, trees, lawn), etc.  

You will need to take a look at what it is you are trying to water - In irrigation design, the base reference landscape material for irrigation management is lawn/turf (alfalfa for farm applications).  

Your goal is to try and replace what is being lost through naturally occurring plant transpiration and evaporation (a value called "ET"), measured in inches of water that need to be applied, either in the form of rain or irrigation (artificial rain).  It changes DAILY, because of weather and atmospheric moisture.  

Here are my basic assumptions of your situation:
-Your home is not a large pasture or alfalfa field
-You don抰 have drip zones, just spray zones
-You just want a basic number for your irrigation timer

IF there is more to your question, see the link below, which can really melt your brain with math, but is good if you want to ENGINEER a system ?br>
https://engineering.purdue.edu/~abe325/week.15/irr.html

(Engineers always make it more complicated than it needs to be, and your question wasn抰 about hydraulic design, but timing.)

First, we need to understand the water needs of your plants.  Plant roots need a combination of both air and water to survive. They actually need time for the water to evaporate and drain away, to be healthy.  Here is today's Indiana ET moisture loss:  http://climate.agry.purdue.edu/climate/et.asp

This site is updated daily.  

You asked about July & August, specifically.  You live in a temperate climate where the normal ANNUAL precipitation exceeds the ANNUAL evapotranspiration (ET), with an average annual rainfall is 40?  From June to October, however, you will need to supplement Mother Nature.  Your lawn is losing about 0.2?per day, and per the Purdue Ag Extension, most lawns in Indiana will need from 1?to 1-1/2 inches of water per week in the summer, depending on weather, soil type, slope, etc.  You抣l need to factor in the 4.2 inches of rain in July, and 3.6 inches August (which by the way, exceeds our total ANNUAL amount of 6.5? here in Nevada).

Never water if the soil is wet! Never assume a plant needs to be watered because it looks wilted.  There is also nothing worse than seeing an irrigation system going off in a rain storm!!

For Indiana*, it is best to apply this suggested amount (1?to 1-1/2? of water in a single thorough soaking, or two equal applications of water three to four days apart during the week, rather than several light irrigations every day. (*A caution to other readers: It is different for other parts of the US)

Check to see if the soil is wet first. Irrigation scheduling is simply a matter of observation and adjusting to the weather. All irrigation systems that I design include a simple rain shut-off ?if yours doesn抰 have one go to Home Depot and get one. They are easy to install.  Ideally, the irrigation control clock should be adjusted on at least a weekly basis to conform with current weather conditions, and monthly adjustments are better than none at all.

When you do water, don't be stingy!  Saturate the soil throughout the entire planter. The soil should be completely saturated to a uniform depth of at least 6 inches, where the primary feeder roots for most plants live.  It is good to cycle your sprinklers.  The water will probably start to run off into the gutter, or into a low spot, before the soil is wet to a 6 inch depth. This is because the sprinklers put out more water in a given amount of time than the soil can absorb. As soon as the water starts to run-off, just turn off the sprinklers, wait an hour or so for the water to soak in, then run the sprinklers again until run-off once again occurs. Continue this run-stop-wait-run cycle until the soil is saturated to the recommended 6 inch depth.   I抳e even dug test holes after irrigation, to make sure the roots are getting enough water.

How to figure out how much water your exsiting system is putting down?  Gen an old coffee can (or 3 or 4), and put a 1-inch mark on it.  Turn on the system, and see how long it takes to fill up to the 1?mark.  Do it for several areas, to get an average.  Voila!  Run your system for that long to 1-1/2 times to irrigate the appropriate amount.  No system is perfect, so you抣l have areas of un-even coverage.

A bit about drip - Avoid cycling drip systems.  The water needs are the same (1?to 1-1/2?per week) .  To saturate the entire planter area, the water has to move outward in the soil from the emitter locations. If you can't achieve saturation of the entire planter area, you at least want the wetted area around each emitter to be as big as you can make it in a single 24 hour period. You may even need to add more emitters to achieve the goal. If you do add more emitters, space them at least 36 inches apart.

Best time of day to water?  The ideal time to irrigate a lawn is from 4:00 to 8:00 a.m. At this time water pressure  is usually the highest, there is little distortion of the watering pattern by wind, and the amount of water lost to evaporation is negligible. With an automatic system, you won抰 have to get up to turn on the hose!!

Remember, the goal isn't to add more water to the areas that are already wet, the goal is to wet more AREA for the roots to grow in.  For further Info for Indiana lawns:

http://www.agry.purdue.edu/turf/tips/turftips.html

Hope it helps. ~Marc