Multiple EPG cron schedules

[cachibachero]

Hello, and thanks for this beautiful work.

How can I add multiple schedules to update the EPG
Let's say every 6 hours starting at midnight.
I used: '0 0/6 * * *' (without ''), but at the moment to save the changes, it displays the error: The sync Schedule must be a valid CRON expression.
Thank you.