Here you go. A smidgen shorter than your whole command line, but all within Perl:

perl -MPOSIX=strftime -MFile::Find -e'find(sub{-f and$t{strftime"%Y%m%
+d",localtime((stat)[9])}+=-s;},".");print"$_ => $t{$_}\n"for sort key
+s%t;'
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