I've been told that if you water the garden during the day, the grass will not absorb it well since it will evaporate because of the sun. However, during the night the plant are not active because there is no sun so they don't use the water? I don't know a thing really, I'm just guessing.

watering in early morning, and or evening befor the sun goes down but is a little cooler

Generally, it will be cooler at night. This will result in less evaporation of the water than during the wamer day. So, more water gets to soak into the ground.

So, it may be marginally better to water at night depending on the temperature difference day to night, and how much area you're going to water. The water savings is probably negligible if you're watering a small garden.

-Guru

Some plants need to dry out to prevent fungus or similar diseases from taking over. By watering at night when the plants are already damp from dew, you allow the leaves to dry out durning the day. But if you water in the daytime they never get to dry out. This is especially true for grass, like a lawn or golf green, but should apply to gardens as well.