It probably depends much on the temps.  Is it hotter or colder than previous years in your area?  What zone do you live in?  Cole crops can grow nicely well into a frost and even covered after that, if you baby them.  I remember snow on the ground at Thanksgiving and we had fresh brussel sprouts. 

You could always start a few outside and see what happens. . . Then you will know for future years.  One of the books I have read suggests black plastic in the spring to absorb heat.  I bet you could use white to shield some of the heat.    Let us know how it turns out. . .I am getting ready to so some planting myself!

I know how the busy factor goes, especially this time of year! 

My chart says Aug 10 but they go by frost date, not zone.  I live in a 5b/6a zone.  I don't think the seeds care.  You could probably get them to start in the house and take them out when they get a a little bigger.  I just saw that the spinach that I planted last week sprouted.  I would think that it would be worth experimenting with a few seeds to see whether they grow.  You can always add more to the garden when the proper chart time arrives. Think of yourself as a researcher and document dates and temps for next year, especially of planting and harvest periods.  That way what grew well,you can repeat next year & stuff that didn't –you might try again, but different care.