Fertilize will be taken up by all growing plants in the plot... your intended plants, as well as unintended grasses and weeds. BUT some weeds are even more preferred than many of the things we plant (especially summer weeds).
I'd be more focused on cost to benefit ratio (fertilizer isn't cheap)....
As such, to get the most bang for your buck, I don't like to put down fertilizer a long time before a rain (due to sublimation and loss of potency, especially the nitrogen component), but I also don't like to put fertilizer down before a huge rain event with the potential for downpours of more than 2 inches in a short time due to loss from runoff. So if you live in west TN, I would be concerned about the possibility of too much rain this weekend.
While it isn't a total waste to fertilize weeds (as the fertilizer taken up by the weeds will eventually be put right back into the soil when the plot is terminated in the future), to get the most bang for my buck, I put my fertilizer down before a rain event 2 to 3 weeks after initial planting and ONLY if I get a good stand of my intended crop.
