For those who have successfully planted food plots for birds, when do you normally plant stuff like sunflowers, corn, milo, millet, peas, beans, etc...?

Sunflowers should already be turned/planted. They have to freeze to produce!
Are you trying to plant on the same property? One field? can you flood it? Are you planting without proof of birds?

A lot goes into it and you often can’t expects results year one! Depends on location as well.
You have given zero factors other than you wants to plant for migratory birds….

The process of seed freezing before it will germinate is called "Stratification". Like pecans and acorns they need to be cold before they will sprout, but according to the seed supplier this seed doesn't require stratification prior to planting.

https://mbsseed.com/product/spring-gamebird-blend-25-lb-bag/

Two plots are planned, same property.

One plot approx 3-5 acres on high ground native pasture (dove plot).

The second plot will be approx 3 acres of moist soil bottomland that surrounds a 2-3 acre pond (duck plot).

The property is proven and has been holding ducks, geese, cranes all season even up until a week ago.

How do you all keep the weed out of your sunflowers

Where are you located? Most CenTx soils have native sunflowers.

Here’s my recipe:

Year one. Plow and then drill peredovik sunflowers in late March to early April.
Peredovik are a hybrid between natives and larger black oil type sunflowers. In sept mow and then plow under. Year two, plow in February and then drill peredovik in March. The tilled under seed will revert toward its original form and then produce a tall native type sunflower. You will also get the peredovik from drilling.

Year 3,4,5,etc just deep chisel plow in February and the natives will explode. You will need to fertilize with a high nitrogen fertilizer every 3-4 years.