In a regular lot in town, or with water for the first few months, all year planting is no problem as long as you plant each section at the same time. You do not want to keep digging holes and watering, in plantings you've already done.
normally lost less than 10% of our plants planting in spring-summer,
even when it is 110 F., but YOU HAVE TO WATER once a week or so to a
depth of at least a foot, preferably 18 inches, and then let the top
1/2 inch dry between waterings.
We've been zinged with fall planting because the plants go into winter, growing, instead of hardening off. We also can have an extended fall with hot dry temperatures and the plants die of desiccation (the site is drier then than in midsummer). Winter planting in a cold winter climate(below 15 F) can be very risky. It takes a few weeks for the plants to harden off, and the plants do not have this time if you plant in the winter. If the plants are dormant or allowed to harden off, i.e., being grown in an equally cold climate, winter planting is easy. Do not worry unless your area gets below 15 F (-10 C) with no snow.
AND, the soil is easy to dig in!
Both the higher temperatures and longer days of early summer have been shown to increase growth of some symbiotic microorganisms while others have adapted to cool moist soils. If the site is a highly stressed restoration site that is getting no water you are forced to do a midwinter planting. In coastal or mild climates early winter planting is preferred, as soon as the ground is moist from rains. If water is available for even two waterings and winter gets below 20 F, on most sites March-April planting is preferred. (Back east that may be May.) In most of California fall planting is the least desirable. This is because the microorganisms and the plants are at their weakest (the site is dormant), soil moisture levels are at their lowest, and the stupid critters eat anything that has green on it. These site conditions will draw from the plant rather than support it.