It really depends on what you are shredding. This year I planted Hybrid Clearfield Sunflowers, popcorn corn for last split. I also did a field in Sesame. It will be ready for the second split. I have done quiet a bit of experimenting with what doves like the best in South Texas. And it has come down to Goatweed hands down. So I do things a little differently than everyone else. I have a 5 acre field next to my sunflowers that I disked and sprayed dual on back in April. Once the goat weed got about 1 foot high(end of May)I disked strips in the goat weed about every 30 feet. That is my supplemental feeding to keep the birds on me all summer. It works great. The goat weed spits the seed in the strips and they are there to pick it up. They will also land in the strips and walk into the Goatweed to feed. Now, in my sunflowers, I have volunteer Browntop millet growing from last year. When I planted my sunflowers on May 1st, I sparayed dual the same day I planted. This delayed the Browntop from germinating which is what I wanted so that the sunflowers could get a head start. Once the sunflowers got about a foot and a half high, the Browntop started growing. The Browntop does 2 things. It matures before the sunflowers and lays down on the ground. This keeps any weeds from growing in your sunflowers. It also puts seed on the ground. So even though my sunflowers are not mature yet, the doves have been going in there eating the Browntop. If there is a few spots greening up come sept 1st, I will hit them with a very strong dose of roundup. 1 week later I will start making runs with a FLAIL mower to chop and put sunflower seeds on the ground. The strips that I do not cut I will save for the second split along with the sesame. 3 weeks before the second split opens I will start flailing strips in the goat weed to keep the birds coming. The Browntop that is left over in the sunflowers that weren't cut is packed right on the ground keeping it clean. Even if it rains, the seed cannot germinate because the sun cannot hit the seeds hidden under the mat of Browntop. Millet will germinate very quickly once cut and hit with moisture. So like I said it depends on what you are cutting. If you already have some birds using the field, put off cutting as long as you can. Birds build up population quick. You can have 5 fields of goat weed all next to each other and all can have birds. You go in there and strip some runs in one of the fields and the birds will leave the other fields for the one with the strips. I've done it and seen it. Farming for dove hunting is a year round thing for me. I have planted EVERYTHING. I've got about 100 birds in my sunflower field at present. They aren't going anywhere. I will start stripping about 10 days prior to opening day. And I won't be stripping much. I wait until I know there is a little col snap coming( especially a dry front) then I will put some seed on the ground big time. It doesn't take much for the first few weeks of the season. I've seen guys use up all there feed the first few weeks by shredding the whole field and then a rain comes and everything germinates. Doves are gone after that. Now, Texas Native sunflowers will not germinate. They have a dormancy that has to be broke by over wintering in the soil. But a hard rain can push the seed down in the soil hiding it from the doves. The natives do work great, I like them a lot. Not to mention that you only have to plant them once. If people only knew how much better a flail mower was for cutting them than a bush hog. Big difference. Sorry for such a long post, just trying to share some of my experience. I could have answered your question with just one sentence, as a rule of thumb, 10 days before opening day is always a good standard. I've had fields that I hunted 4 and 5 days a week. Get in there, kill a limit and get out and let them feed. Every week cutting a few strips to keep seed on the ground. Keep an eye on the birds a few days a week, they will tell you what they want. Keep the ground clean and they will be there.