Someone correct me if I'm wrong. 2-4D is a contact killer and if you spray now to kill it. By the time it's dead and ready to till you will be good to go. I spray a gly/2-4D mix to burn down the garden and also do it in the rice fields.
Seems like a lot of different opinions in here, but this one is more in line with what most do. 2,4-d breaks down in a matter of days in even marginal soil. 30 days after spraying shouldn’t have any effect on new plantings.