goroutine safe.

Field name | Mandatory? | Allowed values | Allowed special characters ---------- | ---------- | -------------- | -------------------------- Seconds | No | 0-59 | * / , - Minutes | Yes | 0-59 | * / , - Hours | Yes | 0-23 | * / , - Day of month | Yes | 1-31 | * / , - Month | Yes | 1-12 | * / , - Day of week | Yes | 0-6 | * / , -.