Most food plotters I know focus on seeding their perennial clovers and alfalfas in the spring. The advantage of that is you capture the early spring rains and the moderate temps that are present before the summer heat sets in. The negative of spring seeding is you also deal with weed pressures. Many farmers have turned to fall seeding their alfalfas as there are less weed challenges and you have more time to do good chemical burndown preplanting. Here is a few options to consider for fall seeding of perennials.
The first option would be to plant a spring soil builder mix. You get the ground covered, helping suppress weeds naturally as well as fixate nitrogen and add organic matter to the soil. This also gives you a preferred food source for the does and bucks when they need it most. You then spray it in the middle of July, til it down and then plant your perennial mix the first week or two of August.
Option 2 would be to plant oats to keep the ground covered. If broadleaves are a big issue for you, this allows you to keep the oats growing from spring through July as you can use a broadleaf herbicide to spray over the top of the oats, killing actively growing broadleaves. Then you til the oats down and plant your fall perennials.
Option 3 would be for people who have grass issues in the field they want to plant perennials. You plant an annual clover blend (soon to be released) and give the ground a fast growing desireable forage source. You then can use grass kiler (clethodim, arrow, select, poast, volunteer) to control the grasses, while allowing the annual clovers to continue to grow and provide ground cover and a forage source from spring through summer.
Option 4 would be to establish a perennial plot with the addition of a nurse crop. When establishing perennials in the fall, you will have less weeds to contend with but you also will not see a lot of tonnage produced from the new seeding. This is where using 50 lbspeas and oats per acre or a half rate of my frosty delight brassica mix would come in handy. You would give a fast growing forage source as a food source to the deer while the perennials are slowly establishing themselves. By spring the perennials are already well rooted and ready to explode with the spring rains and as temperatures heat up.
Again, there are no 1 patented answer that works for all. Look at your own situation and see what weed types you have. What is your deer numbers? What is the weather like for you. This year if your having a hard time getting anything planted, it's not too late to establish perennials, you just might need to wait a couple months to do it. This is a good backup plan.