Learning PHP on your own can be a difficult journey, but it's definitely doable. I would say that it should take abotu a month or two, considering some days you just won't be able to keep up with the lessons. As well, there will be other interesting tutorials you want to do before moving on I'm sure. Let's be realistic as well though. If you're working at another job, and you do this in your free time, it's going to take longer.

It has taken me a year to get to the point I'm at currently (a lot of starting and stopping). I've gone through hours of videos and tutorials that are probably useless to me, because I never found a guide to learn how to build website from the ground up