If the scheduler is not working go through the following checks:

1. Apply the latest patches (/admin/settings/update) and make sure you did a reboot after the updates
2. Make sure the time & time zone are both correct (/admin/settings) and reboot the server after you applied any changes!
3. If you updated LUCY from an older version (< 2.8) the time zone settings that have been applied before the update may not be effective. As a result all mails might be sent at once even though you configured a scheduler. To fix this please re-apply the time & time zone settings again even if they appear correct.
4. Make sure your license has enough credits and is not outdated (/admin/settings/license)
5. Set a scheduler for a campaign with one simple rule (a few minutes in the future), then start the campaign & wait at least one hour to exclude any problems with the accuracy of the time settings
6. Did you start the campaign after setting the scheduler? Please note that setting the scheduler won't initiate the mail delivery. The campaign needs to be started as well.