Using context in trigger interval

When I try to do the next:

{
  "trigger": {
    "schedule": {
      "interval": "{{ctx.metadata.config.interval}}s"
    }
  }
  "metadata": {
    "interval": 5
  }
}

It will not work and throws the error: [parse_exception] could not parse [interval] schedule. could not parse [{{ctx.metadata.config.interval}}] as a [seconds] duration while saving the watcher.
I guess the ctx is also not available at that moment of saving. But is there a way to refer to the metadata to be used in the trigger interval?

The interval schedule does not support reading a variable, you have to specify 5s as a string or 5 as a value to represent seconds as a hardcoded value here.

Side note: The correct way to address that metadata value would be {{ctx.metadata.interval}}