So cron expressions can be as simple as this: * * * * ? * or more complex, like this: 0 0/5 14,18,3-39,52 ? JAN,MAR,SEP MON-FRI 2002-2010 Special characters * ("all values") - used to select all values within a field. For example, "*" in the minute field means "every minute". ? ("no specific value") - useful when you need to specify something in one of the two fields in which the character is all