According to her tweet, “Being told March 17th is currently planned Switch launch day in PAL, will release worldwide that same week but not same date all regions.” Dale also had another tweet which suggested that the Japanese market could get the console first before the rest of the world, which we guess makes sense since Nintendo is a Japanese company and they might want to prioritize their home market first.
Dale writes, “Being told Japanese launch may be a few days earlier but plan is to launch in all major territories that same week.” So basically the Switch could be launched a few days earlier than the rest of the world, it should all be released some time in the week of the 17th of March, which is a Friday.
In any case take it with a grain of salt, but Nintendo will be holding the official Switch presentation on the 12th of January where hopefully more details like titles available, release date, and pricing will be revealed.