0 * * * * /usr/bin/backup.sh
0 * * * * to run at the top of every hour (1:00, 2:00, 3:00, etc.). The 0 in the minutes field ensures it runs exactly at :00.Setting minutes to 0 ensures the task runs at :00 of each hour. Using * would run every minute of every hour.
0 * * * * runs once per hour (24 times/day). * * * * * runs every minute (1,440 times/day).