Other areas of the country is different. Here in the tundra, plow in fall, disk/field cultivate in spring, harrow right before and right after you plant.
If you live in a warmer climate, you can do it all in spring, hope for a rain between the plowing and disking to mellow the lumps.
Plowing in mid summer, beating down the heat baked lumps, lack of rain keeps the ground dry, you hardly ever get a good seedbed.
Too dry, too lumpy, too much heat the seeds like a slow cool damp start.
The tiller might be good to work up your ground now; if you tilled up sod in mid summer, your ground was dry, your ground was hard and lumpy, the tiller didnt work it as good as you thought, sod doesn't till up well or easy, ESP in mid summer.