Disable Graylog Alert on specific time

Graylog Central (peer support)
3

@gsmith Thanks for your reply.
I try to set pipeline rule to do this.
But I want to know how can I set “half hour” in the rule ?

rule "add send alert field to message"
when
  to_long(to_date($message.timestamp).hourOfDay) >= 6 &&
  to_long(to_date($message.timestamp).hourOfDay) <= 7

then
  set_field("disable_alert", true);
end

I found the function “minute of hour”, but I don’t know how to define 6:00 to 6:30.
Any idea ?