When is the best time of day to water outside plants and flowers.?

HI:}
the very best time to water is after 6 or 7 at night when the sun is going down the heat of the day is dwindling .
this way the moisture does not evaporate with the heat of the day sun .
so once in the early evening is the best time .
pj :}

Use an automatic drip system with a timer for mornings and evenings. This should solve your hatred in watering manually.

Evening...the sun can burn them, if you do it in the heat of the day....

Early morning or early evening. During the day, it will just evaporate, and if you wait until too late in the evening, you risk fungi and mold. How often depends on the type of plant and how established it is.

early morning before the sun hits them. Else the sun will evaporate the water before the plant has a chance to absorb it. At night water could just sit on the leaves and that is not good. could get moldy.

When the sun has gone down. Ideally nighttime. There is less evaporation, and hot sun, and water, at the same time, can scald or damage the plants.

Definatley in the early morning, before the sun gets on them. That way they can absorbe the water before the sun evaporates it. But you want the sun to evaporate the water through the day because if the soil and roots are wet at night mold and fungi may grow and kill the plant.

I live in Florida and I water twice a day during the summer. It is 100 in the shade here and the flowers will wilt if they go 12 hours without a drink. I soak them really well in the morning and then give them a shorter drink in the evening 5-7 p.m.

It is not good to water them too late in the evening because the bugs, esp. slugs, will come out in the evening to devour wet leaves. I also keep mulch around the plants and flowers - it is absolutely essential here because it does help keep the moisture from evaporating from the "soil" which is actually sand.

You MIL is correct about twice a day H2O for new plants or seedlings - they need twice as much water as established plants.

Unless you plant cacti, then you can water once a week. :)