The average water sprinkler with a standard size garden hose takes around 30 minutes to water 1 inch of grass.
This has been my experience and when I laid out a can and turned the sprinkler on it took 30 minutes to add 1 inch of water to the can.
So if you need to water 1 inch of water for your grass or garden you would leave the water sprinkler on for at least 30 minutes.
If you have a larger sprinkler or larger hose and more water pressure then you might be able to water 1 inch within 20 minutes.
It depends on the size of the sprinkler, hose and water pressure but for most home water pressure and hoses and sprinklers it takes around 30 minutes on average to water 1 inch of water.