こちらの記事が参考になる
https://blog.dbrgn.ch/2013/10/4/heroku-schedule-weekly-monthly-tasks/
毎週月曜実行
[ "$(date +%u)" = 1 ] && echo "happy monday"
毎月はじめに実行
[ "$(date +%d)" = 01 ] && echo "happy new month"
毎年 12/24 に実行
[ "$(date +%m)" = 12 ] && [ "$(date +%d)" = 24 ] && echo "happy holiday"