On the other hand instead of the first five fields you can use one of the seven special strings that define for you with an easiest way what you want to do. Those strings are the following:
@reboot = Run once, at startup.
@yearly = Run once a year
@monthly = Run once a month
@weekly = Run once a week
@daily = Run once a day
@midnight = Pretty much the same as @daily
@hourly = Run once an hour