There's a trade off, if you water in the evening then you increase the risk of fungal diseases because the leaves stay wet for longer. If you water when the sun is high you lose more water to evaporation (same thing if it's windy). Generally morning is the best compromise. There is an idea that if you water when the sun is high then the light is intensified through the water droplets and burns the leaves and that's why some people avoid watering when the sun is high. It's actually not true, if it was the leaves would get burned every time there was a shower followed by the sun coming back out. In reality if the plants are thirsty, you need to water them there and then whatever the sun is doing.
to NGA.
