The longer between spraying and disking the better. If you get a good kill and wait long enough, the roots in the ground rot. That REALLY mellows up the soil. The trick is to get a good kill. Teacher One's method is what I do.

The idea is to stimulate new growth. Roundup (or most my chemical for that matter) only works on green, actively growing plants. Stuff that's gotten big and dormant will not take in the herbicide.

You CAN spray after hunting season while your plots are still green and relatively short. This makes for great coverage, but you'll likely have to do it AT LEAST once more in the summer and likely twice. I'm too lazy for that.