How to set custom backup frequency?

All other software I tried allowed this, but I don’t see the option in KopiaUI.
It only allows to select pre-defined values, and the field where effective seconds are shown is not editable. Like I want to set 5400 seconds for example.

Below the ‘Snapshot Frequency’ row with predefined values are 2 rows for ‘Times Of Day’ and ‘Cron Expressions’. Both should allow you to set custom values.

“Times Of Day” requires to list specific times, it does not allow to set custom backup frequency by specifying time between backups.

And I don’t understand how to convert “every 5400 seconds” into a cron expression.
According to wikipedia it should be:

*/90 * * * *

To run every 90th minute, but that fails

Can you try this?

This:

0 */3 * * *
30 1-23/3 * * *

Seems to work.

Still, this is an overcomplicated way to do things vs. editing one variable to set an interval in seconds, which is even already being displayed in the UI.