To make the lights be 'static on' you would have to create a non musical sequence that covers the time period that you want the lights to be on.
Then you would simply put a single effect on your lights model like color wash with your desired color across the whole time period of the sequence.
Then in the xLights scheduler setup a schedule to run that sequence every night, 7 days a week, for how ever long you wold like it to turn the lights on.
Since that would essentially tie up a computer I would look at getting a Pi computer, about $50 to setup and let that be your scheduling computer to run the above sequence.
You can find more information about the Pi program and hardware over on Falcon.com.