Help Constructing Cron Expressions
A CRON expression is a string comprising 5 fields separated by white space that represents a set of times, normally as a schedule to execute some routine.
* in the value field above means all legal values as in braces for that column.
The value column can have a * or a list of elements separated by commas. An element is either a number in the ranges shown above or two numbers in the range separated by a hyphen (meaning an inclusive range).