This is what I used for Night 6 & 4/20 (Night 7). So here is my strat: Check both sides, then bring up the camera, only check Cam 1C (Booty Cave) and Cam 6 (Kitchen) back and forth, rinse and repeat. But you have to keep an eye on Freddie. When Freddy is at Cam 6, close the right door. You have to wait until you hear the Freddie laugh again, that means she is not at Cam6. Still check Cam 6 to see that Freddie is there or not. If she is not then open the door. When doing all this you GOTTA be quick! Trust me Night 6 & especially 7, you'll be repeating this strat ALOT, your energy will drain, and this will take some tries.
So hopefully it'll help you conquer Night 6 & Night 7 (4/20 Mode).