I would normally say that those are safe options. Recently, people have been commenting that progress through customs and immigration is slow due to understaffing in and hordes of cherry blossom fanatics. I have doubts that the cherry blossoms are the proximate cause of the crowding, but they're a convenient scapegoat... for another week at least.

If your flight lands at 6;55 AM ... you should arrive ahead of most flights from Asia so I guess you won't be at the back of an enormous queue.

If you are unlucky enough to miss your flight, I think "delayed by cherry blossom fanatics" will probably earn you a seat on the next flight to Sapporo.