You've got a few months. Just keep using roundup (or similar) to kill the weeds as they grow. As long as you spray them before they create seeds, you can till the dead weeds up into the ground. If your current weeds have already gone to seed - kill them with roundup, then kill any weeds that germinate. Just keep using roundup as needed until you're ready to plant. Get yourself a sprayer and a big jug of roundup concentrate for $50. That should last you for the rest of the summer until you're ready to lay sod. Just keep spraying. You'll have to spray a lot over the next several weeks to thoroughly kill the weeds you have now because they are well-established. After that, just spray as needed.

I agree that it would be a good idea to put down a pre-emergent 2-3 weeks before laying the sod as an added precaution,