I think you'd be fine to spray. Weather on our place in north Missouri hasn't been so hot, except for a couple of days, that I would worry about applying herbicide.
You may be getting too close to hot weather to mow, especially using a riding mower, even on the high setting. I think given the possibility of little rain and hot temps I would hold off. Especially if you've got clover a foot or more high. Now if it's just six inches or so, you might be okay because on the high setting you wouldn't be taking off all that much so stressing the crop probalby wouldn't be an issue, but any higher and I think I'd wait for cooler temps and increased rain possibilities.
Don't expect the Arrest to kill all your grass. Even after our second application of Poast Plus (same as Arrest) we still have grasses. Plus, as the grasses get more sparse, it seems the weeds take advantage of the opportunity and really start to show themselves.
Best of luck, let us know how things turn out.
“There are two spiritual dangers in not owning a farm. One is the danger of supposing that breakfast comes from the grocery, and the other that heat comes from the furnace.”