I don't have an answer because I never measured but just wanted to let you know OP that sometimes knowing how long it took others can be discouraging to you instead of inspiring. If your hair grew slowly and someone told you that she got that growth in a few months, then you would feel like you're doing something wrong if that wasn't your story. So rather than be so preoccupied with "how long", I always tell people to focus on perfecting their regimen so that they get a steady growth and good retention and discover all the many things your hair can do and have fun.
How long it took to get there won't matter when you get there. Just that you made it is all people will notice. A watched pot never boils. The sooner people realize this, the more fun they will have with their hair and the more wonderful surprises they will encounter on this journey.
I've been here for a looooooooooooong time and granted I don't take this journey as seriously as some, but I still want long hair. And when I get to a milestone, trust me, I never wonder how long it took to get there and most times I discover it just by chance...like I'm fingercombing a braid section and then discover I can actually look at it as I work on it.
So stop looking to others for answers about YOUR hair but let your hair show you what it's about.