Usage: ./git-commit-modify-last-time.sh <seconds(like: 86400 = 60 * 60 * 24 (s) = 24 (h)>

git-commit-modify-last-time_mac.sh

#!/usr/bin/env bash
git stash && \
date=$(date -r $(expr $(date '+%s') + $1) +%s) && \
rm -rf "$(git rev-parse --git-dir)/refs/original/" && \
git filter-branch --env-filter \
"if [ \$GIT_COMMIT = \"$(git rev-parse HEAD)\" ]; then
    export GIT_AUTHOR_DATE=\"$date\"
    export GIT_COMMITTER_DATE=\"$date\"
    export GIT_COMMITTER_NAME=\$GIT_AUTHOR_NAME
    export GIT_COMMITTER_EMAIL=\$GIT_AUTHOR_EMAIL
fi" && \
git stash pop