This is a Symfony2 bundle that wrappes mtdowlings cron-expression library. See https://github.com/mtdowling/cron-expression
A CRON expression is a string representing the schedule for a particular command to execute. The parts of a CRON schedule are as follows:
* * * * * *
- - - - - -
| | | | | |
| | | | | + year [optional]
| | | | +----- day of week (0 - 7) (Sunday=0 or 7)
| | | +---------- month (1 - 12)
| | +--------------- day of month (1 - 31)
| +-------------------- hour (0 - 23)
+------------------------- min (0 - 59)