Depending on what type of weeds you have, you may have to do two seperate applications. One for grasses & the other for broadleaf. We use Clethodim for the grass & 24DB for broadleaf, and usually wait a week or two in between.
Since this is a new plot, you may also have to spray a couple more times between now & fall. Mowing can also be utilized as well. You'll really just have to figure out what works best for your situation.