This is one of the most common pitfalls when managing crontabs. By default, adding an asterisk value in a time code means that it will run for every instance possible for that value. For example, a value of 0 12 * * * will tell cron that you want to run a command once a day by 12:00 PM.
However, most beginners often write the same time code as * 12 * * *. Writing it this way will mean that the command will run once a minute from 12:00 PM to 12:59 PM. As such, it is good practice to write 0 in the minute field to make sure that the command only runs once.