I guess Nintendo will provide us with some official numbers at least they should if not fu** it.

i say 10 days

I'm going with 1 week.  Japanese gamers will surpass 1m levels in less than 2 weeks time.  I remember the NSMB2 coin challenge.  Never challange Japanese gamers to do something in game because they will go above and beyond.

Easily in 2 or 3 days.

A week. Mario Maker it's a Mario game, a level designer fans have been asking for for years, during a period  of somewhat software drought on the system. It will reach the million quickly, and with that, it will reach the million levels created in less than a week, specially if Nintendo doesn't start banning levels due to "inapropiate content" (penis level joke incoming).

or the same time it takes for someone to shoot themselves in the head after reading all the stupid comments on youtube.

Around a week.

Well, however many units it sells, you're going to have the same number of "my first level" uploads almost instantly.

Probably between 5 days and a week.

1 week if the review/ban control is quick enough on Nintendo side!

I say 5 days