Re: Seriously, there's nothing wrong with the timeline. Read.
I never really saw it as a timelime issue, it's just by Kishi making this clear, allows us to know more correctly, when the 1st war started, and thereby when Hashirama died. It also allows us to know, how long Tobirama was hokage.
IMO, I thought it was not the case that Hashi ever knew Tsunade, simply because it makes Tobirama's time as hokage very short.
Databook states pretty clearly that Hashirama died before the 1st war, and they also state that the war started right after Tobirama became hokage.
This is also logic. Hashirama was a beast, and none wanted to war Konoha during his regime. Also he wanted to maintain peace more than anyone else. With him dead, the other nations no longer feared going to war against each other, or Konoha for that matter.
However, my issue with this, is that picture of Tobirama, Hashirama, and young team Hiruzen. Hashirama doesn't look much older, than he looks in his edo tensei form. Tobirama, however, changed a lot. Of course, Hashirama might just have reached a point, where his physical form didn't change any further, like the end of puberty, lol..
Still, it kinda spits on Tobirama. IMO he couldn't have been hokage for more than a year, if Tsunade should have a chance, to have known Hashirama. And she still needs to have been at least 3 or 4 years old. So Hiruzen kinda had to be, let's say 22 years old, when he became hokage, then it matches if Hashirama died 1 year before this, making Tsunade about 3-4 years old, so she could talk and remember Hashirama.
It's just, the reason many "time-line" creators, will have trouble with this, is that they would assume Tobirama couldn't have made Police force and academy, plus start a war, make peace negotiations with the 2nd raikage, where he had a fight with kin/gin bro's and nearly died, and then later be killed by the kinkaku force.
But now Kishi cleared this part of the timeline, so all these events should probably happen in the first year of the war.