I suppose I could define timed actions to "gate" the behavior of the script using explicit variables (i.e. define "ItsLightOutThere" and have it be turned on and off on a scheduled basis)? Is there a better way?
You are on the right track, but there is a better way that doesn't require variables at all. Use the "Enable Trigger Action" and "Disable Trigger Action" Action Types. Create a new Time/Date Action (or two if you want sunset and sunrise to be the trigger times), set the Action Type to either "Enable Trigger Action" or "Disable Trigger Action" and select your original Trigger Action as the target.
The variable approach might be best if you have a bunch of trigger actions that need the extra conditional. You could create a "myIsDaylight" variable that gets set before sunset and after sunrise, then use this variable in all of the Trigger Actions.