usually how early in advance you all book your flight tickets and hotel for sakura season. since the info for the bloom cant be predicted so early. I am looking at end Mar to early April next year. Hopefully can catch sakura!
Most typical seasons, the 1st bloom is around the mid 20s of March and the full bloom is usually 1st week of April. It is definitely too early now to tell. If possible try being there for a 2 week period in April and it should give you a good chance of catching the full bloom of the somei yoshino and catch some late blooming varieties such as the Yaezakura.
This year's Sakura was a little early due to the warm winter caused by the El Nino. And following the El Nino comes La Nina. The opposite weather phenomenon to El Nino, meaning a lower than average ocean temperature which may bring a colder winter and thus a later Sakura season. You can check the weather end of this year and see how the winter in Japan pans out.
For me I booked my tickets in September as I was redeeming miles during the Sakura season and I would consider myself lucky to hit the right window. I remember being particularly anxious when the weather started to warm up and early bloom of Sakura was being forecasted.