I've already pre-ordered Animal Crossing New Horizons and downloaded it to my switch. The official page now says:
"If you pre-order Animal Crossing: New Horizons, the game data will automatically be downloaded to your Nintendo Switch console before the release date. The game will be unlocked at midnight on March 20, 2020, so you can get started!"
The last part confuses me a bit, today is March 19th, so it will be unlocked at midnight tonight, or do I have to wait until midnight tomorrow?
I guess that means the time from March 19th to March 20th. So they mean the beginning of March 20 at midnight. At least that's how I understood it.
You can play on March 20th, 2020 at 00:00.
Although it took me a few minutes for the game to be unlocked.