Certified GKH Gardening Expert
I'd say that right now is your perfect window for applying pre-emergents! The clay doesn't, necessarily, contribute to weeds, but it doesn't help things out either.
There are ways to amend the clay soil to help it to be better suited for planting, though. This article will help: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/how-to-improve-clay-soil.htm