This is another name for scheduled messaging. The whole idea here is that Jirassimo will not react on specific events in your host JIRA, but rather poll it at specific times and send messages about issues that are relevant to JQL.
To save your time, here're the most popular CRON expressions that you might find useful while configuring your own messenger:
|0 0 10 ? * MON-FRI||Run daily from Monday to Friday at 10AM|
|0 0 9 1/1 * ? *||Run daily at 9AM|
|0 0 12 1/1 * ? *||Run daily at 12AM|
Our messaging system is implemented in such a way that at the beginning of every hour it checks all custom scheduled messengers to understand which of them are eligible to run during this hour. If specific messenger is eligible, then it will be run right away. You should keep in mind that since messengers are run hourly, then it doesn't make sense to use a CRON expression like this (running messenger every 10 minutes):
|0 0/10 * 1/1 * ? *|
If you still do, the corresponding messenger will still run only once per hour.