I've been playing just less than 2 months and am quite comfortable on stage 4. I haven't practised every single day nor do I follow his schedule word for word. Some days I will sit and do an hour of 1-minute changes, chord quality, strumming patterns, etc and not even play a song. Other days I will sit there practising songs for an hour or two without bothering with the boring stuff.
I like the structure of the course but don't want to go through it in such a set pattern that I feel I'm being forced to do something I don't want to do otherwise I'll just get bored. I think one minute changes are great and I really notice the difference but I just hate doing them, I find I put too much pressure on myself to go quicker each time and the quality of my chords is effected.
There's nothing wrong with how you're learning, I've looked ahead myself and briefly looked over some topics. That's it though, it's all been very brief. I've not dedicated any proper time to anything past my recommended stage as I feel it will all come in good time. Just go at your own pace, like others have said, there's no rush to finish the beginners course. The skills you learn can be with you for life if you want them to be, I'd rather take my time with the foundations rather than rushing to the interesting stuff and then feeling disheartened.
At the end of the day, I know I only know very basic techniques at the moment, but as long as Justin says that I'm up to the level I should be then I'm happy. I genuinely feel confident with my progress and already my songs are starting to sound good (in my opinion). I probably could move onto stage 5 right now easily but I'm quite satisfied knowing that I'm really hammering the stuff I've been taught up to now rather than being overwhelmed by lots of new techniques.