The Corn Gluten Meal needs to go down about 6 weeks before those annual seeds germinate in your area.

How do I find out when they germinate. My main target is Annual Bluegrass.

From my reading, poa is actively growing when temperatures are 70 degree days and 50 degree nights. Logic tells me that germination occurs at the beginning of the optimum growing season. You can probably find county climate data for your location to get the average date of that temperature range.

I hope CGM works for you. Let us know your results.

This plant starts to germinate when the nights are cooler (60 degrees) and moist. The article linked below from Texas A & M may be of some help.

Here is a link that might be useful: TAMU about Annual Bluegrass

I would suggest the first two weeks in Sept., or by the 15th. My thinking is that with hot weather the weed seed germination will occur sooner.