i'm sure you've already found it, but yes, it's any night above 2 on the cam where Chica dresses up.
how about night 1
and how about night 2
and should i just spam on and off the tablet
1. its random
2. Try more aggressive nights (4 - 5)
3. Flip to a different can before putting the cams down, then flip back towards the dresser cam (repeat)