As a starting point, git log --format=format:"%at %H" | sort -nr gives a list, with the oldest entry first, of just "hash timestamp" pairs, one per line.

As a starting point, git log --format=format:"%at %H" | sort -nr gives a list, with the oldest entry first, of just "hash timestamp" pairs, one per line. You can then use e.g. date -I --date='@1620720025' to convert the timestamp back to a human-readable date in ISO format, i.e. "2021-05-11". The next step would be to loop over the list, checkout each revision, grep and wc the TODOs, and collect into date buckets. Anyone? :)