Checker now up at
http://project-gc.com/Challenges/GC3C0H5/16116
Note that it is limited as the caches must be 'genuine' puzzles, which is not easy to do automatically. It also does not check that at least one of the qualifying caches is found after the date of the challenge publication.
Many thanks to mole125 modifying his checker script to enable checking the weekday of dates.