The Japan Meteorological Agency announced this afternoon that the cherry blossoms at Tokyo's Yasukuni Shrine are now fully open. Normally the conditions ideal for viewing continue for around a week, so the weekend of April 5th and 6th should still be fine for viewing.
From previous experience, the Sumida Park near Asakusa is always a few days behind other areas of Tokyo.
Neighboring cities like Yokohama are also a few days behind Tokyo, so there will be more chances to view the blossoms by doing a short excursion.