Thank you for your question.  There are several reasons why watering in the morning is recommended.  First, plants only photosynthesize during daylight, so that's when they utilize the water.  Second, some evidence indicates that sun scorch may occur when droplets are on the leaves that sunlight hits.  (This is not a universally accepted theory.). The third factor is that we live in the fungus capitol of the world, and fungal spores grow when they land on plant tissue with moisture on it.  A well known example is black spot on roses, but water accumulation in the soil attracts diseases that promote "root rot".   Here is more on the topic from OSU:  https://extension.oregonstate.edu/sites/default/files/documents/12281/wateringtips.pdf

Hope this is helpful.

Here are some other resources on time of use on watering:  https://www.epa.gov/watersense/when-its-hot#:~:text=Facts%20about%20Summertime%20Overwatering&text=Experts%20estimate%20that%2050%20percent,use%20outdoors%20when%20it's%20hot.

and  https://www.oregonmetro.gov/tools-living/yard-and-garden/garden-basics/watering-tips