I haven't played this game in over a year, and completely forgot I ever posted this until I got your notification. Also, I'm very fucking wordy so sorry if this ends up being a long read, lol.
To put simply, Freddy's AI is a bitch, and none of what I can recommend will work every time.
She moves at intervals that I can't remember, and I know this because I used to use a speed-run timer, and I noticed Freddy always moved at certain periods of time throughout the night. I discovered this after making the guide however, and I never remembered to update it.
From what I remember (which may be wrong), Freddy's AI works in two ways:
- If you open the camera while the door is opened, she will enter your office automatically.
- If the door is open, and she reaches a movement interval, she'll enter your office regardless of if the camera is opened or not.
The closing of the door while opening the cameras is necessary because it prevents her automatic entry.
The second condition is unpredictable unfortunately.
When I beat the night, she happened to reach this interval while I was checking the camera with the door closed, which allowed me to keep it open for the rest of the night and saving me a lot of power. But if you are dying at 5AM to Freddy, it's because she's reaching the interval while you're in your office and not checking the camera- I'd assume.
I recommend one of three things to try predict when to shut the door at her interval:
1. If you are good at multitasking, count from the start of the night and keep record of the times between each of Freddy's movements. This means once Freddy reaches the final room, you should theoretically count down from a number similar to the other counts and then keep the door shut, predicting that Freddy moves again at that rough time.
For example, let's say Freddy has 5 movements until she reaches the final room;
She takes 40 seconds for her first movement, 35 for her second, 37 for her third, 43 for her fourth and 40 for her fifth and now she's outside your office.
You would then count to a number roughly around 40 (pushing the time to be longer or shorter based on how risky you want to be) and then shut the door until she moves again, to which she'll move backwards and you don't have to worry about her again for likely the rest of the night. If she does move forward again, repeat this.
2. If you aren't so good at multitasking, you can use a timer software such as LiveStock, which would allow you to record Freddy's intervals without the need to count, but it does take some setting up and you may need to use a few Youtube videos to get a handle on how it works. This also really only works for PC.
You could probably even find a timer app on your phone if you wanted to as well, though I don't know of any to recommend.
3. Without a count for her intervals, the only other option is to guess or get lucky. You either keep retrying until you get lucky and Freddy moves while the door is shut and you're on the camera, or if your gut feeling tells you it's been long since Freddy has moved, shut the door and pray she reaches her interval in at least the next fifteen seconds, or else you're wasting power.
Everything I've written prior is mainly applied to 4/20 since it's much stricter (and at that, it's still a pretty shit guide for 4/20), but you mentioned you're on Night 4.
I'd assume these strategies could still apply, but I reckon you could bullshit your way through it by just keeping the door shut after 5AM to be honest. Of course I might be wrong, but again, it's been a year so I wouldn't know anymore unfortunately.
In conclusion: No, you haven't misunderstood anything and it's not a glitch either. Freddy's just a dingus.
Hopefully this wasn't too confusing to read, and also, I hope it helps.
Good luck.