Keep the monitor up on pirate cove and only lower it to close the doors, wait no longer than 2 secs for Bonnie and 1 for Chica (then immediately lift the screen back up). I was able to keep Foxy behind the curtains up to 3 am!
It takes 1 minute for Foxy to enter your office and keeping your eyes on her is the only thing that stops that timer. Watch out for power tho, but you really want her to consume screen power rather than eat your power by bashing the door.
Also, try to keep her from running into your door more than once.
Good luck!