There's an easier way to do what you want. Set your polling intervals to defaults and levae them there.
Create two sets of alerts. One for the daytime which alerts based on defaults. Use the Time of Day tab to suppress those alerts at night.
Create an equavalent nightime alert that and then set up a sustained-state trigger condition. To set up a sustained state trigger, at the bottom of the Trigger Condition tab, provide an appropriate amount of time the alert engine should wait before any actions are performed. In your example, it would be an hour.