"Opening"(開花) is defined as the condition that at least 5-6 blooms are observed at the standard reference tree in each region. Reference tree in Tokyo is in Yasukuni shrine. From mid-March, persons from Japan Meteorological Agency (JMA) come to Yasukuni shrine everyday and if they find blooms, they declare "opening" of the year.

You can usually expect a little bit blooms everywhere in Tokyo within three days from the “opening”, 60-70 % blooming within a week, which is reasonably beautiful and I like it better rather than full bloom, and full bloom within 10 days.

But even before the standard Yasukuni shrine tree, of course there should be some trees start to bloom. I remember cherry trees near the front gate of Waseda University have always a few days earlier blooms than most of areas in Tokyo, although there are not impressively many trees there...

Enjoy !