I only water in the morning if they are showing signs of being too dry. So if it has been very windy I will water in the morning, but usually only at night. I often do a watering at 6ish then again a couple of hours later. so this allows the compost to hold more water overnight.

I water morning and evening because the weather has been so warm and our soil and tubs just seem to dry out so quickly.

If you're talking about hanging baskets, morning and evening is best in hot weather - some smaller containers too may need this, but generally, its always best to wait till the top of the compost is slightly dry and then water thoroughly. Same with the ground - watering well (half an hour with the sprinkler) every 5 days on newly planted things is much better than watering daily with small amounts.

I usually do the main watering in the morning, so they are well moistened during the hottest part of the day. Those that need a second watering get it in mid afternoon--if I can!