How Cron works:

<Minute> <Hour> <Day_of_the_Month> <Month_of_the_Year> <Day_of_the_Week>

* * * * * *
| | | | | | 
| | | | | +-- Year              (range: 1900-3000)
| | | | +---- Day of the Week   (range: 1-7, 1 standing for Monday)
| | | +------ Month of the Year (range: 1-12)
| | +-------- Day of the Month  (range: 1-31)
| +---------- Hour              (range: 0-23)
+------------ Minute            (range: 0-59)

Examples:

0 0 * * * *                         Daily at midnight

5 minutes after midnight each day

05     0      *       *       *       root