I think it was between a week and a month. I'm actually not sure because it was so long ago, but I do remember that I wasn't very successful. I hadn't heard of lucid dreaming at all and knew nothing about it, it had just happened to me a couple of times and I tried to make it happen again.

Years later, when I did stumble across something on lucid dreaming online, and found out that it was something people had named and studied, it took me about two nights.