Personally after the Wii U debacle I don't thunk it's enough time but they might prove me wrong. We'll see.
Wii u was advertised for 15 months and a lot of people were bashing the console for 15 months too, so time is not important here, the important thing is the execution. ps4 and xbox one were heavily advertised after e3, that's 6 months. If the NX is advertised the right way with the right games, it's enough. My opinion of course, I don't have a marketing degree.