Remember you can restart the level clicking the donut (save yourself the time of actually losing on bad terms)
Literally kept the screen up in Pirate Cove as long as possible (I feel like switching it doesn't work as well as just keeping it up) and if Foxy goes running before 3 AM, restart the level. So, without checking the camera, Foxy takes about 1 minute to run inside the office, but keeping your camera on Pirate Cove actually stalls her.
You should try keeping her behind the courtains so that she only rushes you once. If you see she already left the Cove, don't even check the hallway; take the chance to lower the screen and just wait with your cursor over the left door button (close as soon as you hear running footsteps). That way you'll save valuable amounts of energy.
If you reach 4 AM at 25% you'll have a chance of winning (if you got -20%, restart) if Foxy is still in Cove.
Good luck!