From b2evolution manual

Scheduled tasks are queued in order to be executed asynchronously. This has two advantages:

1. It prevents you from waiting for longer operations to finish while you use the application (e-g: pinging remote sites after posting)
2. It allows for automatic execution of maintenance tasks (e-g: updating the antispam list every day)

Existing scheduled tasks

• Poll the antispam blacklist
• Prune old hits & sessions
• Prune old files from page cache
• Create posts by email
• Process hit log
• Unread Messages Reminder

[edit] Setting up the scheduler

For the scheduler to work, you need to make sure /cron/cron_exec.php is called on a regular basis, such as once every few minutes.

There are several ways you can achieve this. Here is a list in order of preference (first is best):

• Set up a Linux cron job i-e: let Linux call php on a regular basis
• Set up a cpanel cron job i-e: let "cPanel' call the scheduler through the webserver on a regular basis
• Set up a Windows Scheduled Task i-e: let Windows call cron_exec.php on a regular basis
• or Set up a web watch dog that will ping http://example.com/blogs/cron/cron_exec.php regularly
• or Open that page in a browser and let it refresh itself.