Again, here we can rely on zsh having advanced globbing functionality. Instead of moving your test in to the execution block and suddenly having possibly unbalanced parallel groups you switch to something like *(.mw-1) to operate on files(the .) modified in the past week(the m[odified]w[eek]-1) or whatever. I'm choosing mtime because of your %Y, but zsh offers many other filters too. This is detailed in the glob qualifiers section of the zshexpn(1).

I'm not sure whether I'd move the actual branching in because of the balancing issue, that is point where my hairs stand up. Perhaps, this is where it all falls apart.