It's a bad idea to water when it's windy, so that's one time to turn the sprinklers off. Another time that should be obvious (but seems to escape most of my neighbors) is if it rains. I take it a step further and turn off the sprinklers if rain is forecast in the next couple of days.

My irrigation system is probably off more than its on. Here in FL you never really know when an afternoon storm is going to pop up. I just leave it off until I know the grass needs water. One way to tell when your lawn needs water is when 30-50% of the lawn shows signs of wilt. When I do water my lawn, I run my irrigation between 12am-6am.(less/no wind and no sun) Irrigating during the late morning and afternoon will waste irrigation water to evaporation. (Plus wind)

I'm with skoot cat and BP. About the only time I run my timer is when I'm watering up grass.

Leave it off and worry only about the better question, when to turn it on. And skoot nails that.

Automatic timers are a great convenience, but, really probably hurt the grass more than they help and, as the original poster noted, wind up wasting a lot of water.

The above posters are knocking the ball outta the park!!!

The better question I think is when to turn the irrigation system on. Just my opinion here but I tend to think automatic timers do as much harm as good.

Controllers should be utilized when out of town and to water manually. I rarely leave mine in the automatic position. Water less often, yet for longer duration up to the point of soil saturation.

Thank you so much for the wonderful advice! Turning off the system is at the top of my to-do list for tomorrow.

My system is never on a schedule, so even though it's technically "on" it's off. When I want to water I just set the day or do a manual setting, and then when it's done I delete the day from the program.

digging dee, it is possible to have the better of both worlds. Everywhere in Florida (I believe), a rain shutoff is mandatory for automatic systems. So when it rains enough, the system is shut down.
'Atmospheric stillness' is one of the reasons why irrigation is programmed for early in the morning.

I disagree a controller is a great way to save water and to control water waist. The issue here is that the sprinklers were not coming on at a good time to irrigate. You should always run your sprinklers in the early morning. The wind is not blowing in the early hours and also it will reduce the chance of fungi infecting your lawn. You can always add a rain sensor and a wind sensor that will turn off your controller in those situations.

Here is a link that might be useful: when should i water