Indeed, and what a partial world of difference. Thanks for your guidance here. I have pressed my forehead to the fortress wall and walked the perimeter until I found a skeleton key hanging from the lock in this portcullis:
Accepting the limitation implied by "will generally work anywhere since at midday GMT, the entire world (almost) is on the same date", the following emendation to my all-KM macro should work "generally": replace the final Action with:
<img src="/uploads/default/original/2X/1/115538b59fb56972624656d5dfe32558a357a310.png" width="699" height="151"
It remains to make this work globally. Does the KM Calculation "GMTOFFSET()" accept any argument? Is there a way with KM to determine the GMT offset for a given date?
My thanks again. I shall, given the chance, show others these paths.