Not disagreeing, but I think it would be simpler to apply your crabgrass control now. Normally it should go down before the temperature hits 80 degrees, but this year has been so strange, best to apply it now to be sure crabgrass doesn't get ahead of you. Growth of the good grass will not be too fast if the weather remains cool...if. Try to find a crabgrass product that is high in slow release nitrogen--more costly--but better for the grass. Weed and feed in June...and again in late September. You want to be sure no weeds can get a start AFTER your fall weed control. A good fall weed control means--no weeds in spring.