Thank you for your input!
Honestly, since we don't have year-round trapping season here, the latest I've ever trapped a kestrel was January 14, when our season went until then. I'd say if you could find either an unmated adult bird, or an unpaired passager, go for it. I have trouble hawking kestrels when it's warm out, since they tend to go after bugs...but I know many others who've flown in warm weather with them, and have been successful.