Hola Anne

It might be better to have your sprinklers turn on at 4:30pm so that the heat of the day doesn't evaporate the water. Of course, zones that have plants that are susceptible to mildew such as roses would be better watered a bit earlier to give the leaves a chance to dry out before dusk.

Terran

If you concentrate on watering the soil rather than overhead watering of the foliage, evening watering is perfectly fine. As a matter of fact, you can water in the heat of the day (and not waste water) if you water at soil level.

Just out of curiosity, your irrigation system isn't watering every morning, is it?

Yes, the sprinkler system is set for 15 minutes every morning. But the garden is 2 weeks old, and I have been dealing with some wilting. I have started hand-watering the more delicate plants at soil level which is quicker and does a better job of watering what needs to be watered.

Is this OK?

the idea is that short, frequent waterings lead to plants that cannot withstand even minor droughts because they develop roots that look for surface moisture. A 15 minute watering with any sprinkler system I have ever seen is only enough to water the top 1/4" or so of soil.

If you have seeds or seedlings this sort of watering is fine since they don't have good roots yet, but for mature plants this sort of watering is counter productive even for newly planted ones.

Think deep, infrequent waterings. By deep I mean 1" of water or more. How long that takes varies, but you measure it by placing a soup can or similar shape container in the watering area and time how long it takes for the container to fill to 1". In most cases this should be the amount of water to provide at each watering.

By infrequent I mean only water when the plants actually need it. Determining this is a combination of factors like the water needs of the plant type, how quickly the soil in your yard drains and the outside temp and precipitation levels.

The wilting could simply be that your shallow watering is never getting to the roots of the plant, it is like you aren't watering at all. Try running the system for an hour or two and see if they don't improve overnight.

As for time of day I am of the opinion it doesn't really matter unless your area is prone to fungal problems in which case morning is best as the leaves are dried as soon as the sun comes out, but there is still time for the water to seep into the soil. If your area is prone to fungal issues then evening is the worst time as the leaves will stay wet overnight.