I like Durana white clover and this year I'm going to mix in some Patriot white as well. Late August is too early IMO for this area as the chances of heat and dry weather can kill the new sprouts. I would wait until mid to late September depending on the forecast.
Are you going to till or disc the ground? If so I would spray as soon as possible and once everything is good and dead then till or disc. This is going to turn up a lot of old weed seeds which will sprout given a little moisture. At that point it should be sprayed and tilled again. Repeat this as many times as you can before planting to cut down on future weeds.
I'm doing a new food plot this year. I began spraying in June and just did hit it with the disc again on Saturday. Hope to spray and disc two more times before planting.