Generally speaking, watering in the middle of the day won’t harm plants, however it is usually discouraged due to the higher evaporation rate of water being applied to the plants.
The people on this forum reside in many different areas, types of climates and even within their own property, microclimates. There are so many variables, there is no “one size fits all”.
I don’t water during the middle of the day here in the Sonoran desert due to the high evaporation rate. Best practices dictate that a more efficient time to water is in the wee hours to avoid the hottest time of day. Since the night time temperature can at times, still be in the high 90s, best practices indicate I should water when it’s cooler–like the chilly 83 degrees we experienced at 6 a.m. this morning. In other climates, it may be OK to water at night.
@Ed3120 is in New Jersey and the Cooperative Research & Extension service at Rutgers provides this publication: Best Management Practice For Watering Lawns
http://www.landscapedevco.com/Practices_for_Watering_Lawns.pdf
“Time of Day
The most efficient time of day to water is late evening
through early morning (between 10 p.m. and 8 a.m.). It is
generally less windy, cooler, and more humid at this time,
resulting in less evaporation and a more efficient appli-
cation of water. Water pressure is usually better at night
resulting in a more uniform application of water through
sprinklers. Contrary to popular belief, watering at night
does not stimulate disease development.”
Source:
Rutgers Cooperative Research & Extension
N.J. Agricultural Experiment Station
Rutgers, The State University Of New Jersey
New Brunswick