This is probaly the number one quetiona asked. The answer isn’t a simple time or number.
1st try never to water late evening or at night. Humid moist thatch and soil can be the perfect recipe for disease and fungus.
2nd soil is best if watered to moist not flooded or over drenched. It is even ok for lawns to dry out a little. When lawns dry out the roots search for water by going deeper. This builds a better plant. So over watering or water too often can lead shallow roots. Most people want to set an irrigation schedule in May and forget about it. This is better than nothing but far from perfect. When it is hot out water more when we get rain or cool temps’ water less.
I prefer to water early morning and then when I get home if lawn looks or feels dry, I water again (yes in the evening but early evening). Try to water 2-3 hours prior to sunset. This allows the thatch and soil time to dry out. Also, when you cut your lawn in hot weather always water after cutting even if it’s just few for minutes.
It really isn’t difficult; walk across your lawn does it feel soft & plush or does it feel dry and brittle. Remember; if a lawn does dry out for too long it goes into stress or drought stress. After you start watering, it will take twice as long to come out of stress. This can be a long time 2-3 weeks. During which other lesser issues strive. Weeds, disease and fungus love a stressed-out lawn.