Use this command instead of git commit to commit between two dates

gcd

#!/bin/bash
git commit "$@"
current=$(date +%s)
# Yesterday at 6pm UTC
start=$(($current - $current % 86400 - 3600 * 6))
# Yesterday at midnight UTC
end=$(($current - $current % 86400))
nextEnd=$(($end + 86399))
commitDate=$(( $start + $(bc -l <<< "$(($current - $end))/$(($nextEnd - $end))*$(($end - $start))" | awk '{print int($1+0.5)}')))
echo "$(date -r$start) < $(date -r$commitDate) < $(date -r$end)"
export GIT_COMMITTER_DATE=$commitDate; git commit --amend --date $commitDate --no-edit