Why not just use Do Not Disturb and keep the phone by the bed?
Because the problem is you opening it, not it interrupting you. Do Not Disturb solves the second one and leaves the first one completely intact.
Does greyscale actually work?
For a lot of people, yes, for a while. It won't hold forever, which is why it's week two of eight rather than the whole plan.
I read on my phone in bed. Isn't that fine?
Reading is fine. The problem is that a reading app is one swipe from everything else, and at 11:30 that swipe is very cheap. If you read a lot, an e-reader without a browser genuinely solves this.
Should I use the 30-day version instead?
If the phone in bed is a ten-minute habit rather than an hour, yes — go faster. Eight weeks is for people who've tried the fast version and found themselves back on it by day nine.