The March 2016 notice has returned on the English Miitomo site after it was removed unexpectedly last week.

The reason for its removal is still unknown and it had left some people thinking that it could indicate a delay of Miitomo’s release in the West. However, it looks like the launch will still go ahead this month as planned. Miitomo has already been rolled out in Japan and topped one million users in just 3 days of launch.
US site now also says again: "Launching in March 2016".
For some other regions/languages it says "Planned for".
— Dr. Serkan Toto / Kantan Games Inc. (@serkantoto) March 28, 2016
Thanks, MasterPikachu6

There are only 3 days left in March though…
True, but there’s still time! :)
hopefully using ever last minute to make sure the launch is a success. nobody wants a buggy/busted app
My guess is they had a last minute snag and decided to play it safe with the release date then found the problem was easier to fix than they initially thought.
This reminds me of the long awaited SFV March update that we are finally getting RIGHT AT THE END OF MARCH lol
They figured out awhile ago that they aren’t good at launch dates, so they stopped naming the day in the month of release, and worse case scenario, they don’t even name the month of the season in the 4th quarter that the game was promised. I knew 2015 was too soon a release date for The legend of Zelda: Wood carven Prince.
i’m guessing that this is an app that you can get on your phone.