I believe Reggie or Miyamoto said the expected port time was 1 year on average. So 9 months isn't bad. But yeah it's going to depend on how many assets needs to be redone, team size, and the skill and experience of the team that is porting. 

Actually its not, its normal time of porting game, development of new game today usaly is around 2-3 years with hole teams behind, ports are usualy done buy much smaller teams and they are usualy done in less than one year. PS3/360 hardware on mind dont change much beacause we talking about huge game with plenty of content.

Yeah but Diablo 3 with all DLCs has huge amount of content, we also dont know what was size of team behind port.

No on average, they said less than one 1 year, and they are right.

People need to have few point on mind, today new game AAA development usually lasts around 2-3 years,
porting existing AAA game last less than one year in most cases it seems 8-9 months and buy much smaller team and with much smaller budget.
So no, 9 months for port of game of size of Diablo 3 with all DLCs is not long.

All we know now is how long Blizzard needs to port exactly Diablo 3. And while Diablo 3 is a big game it's a completely different beast to other AAA games. So no, we still have no idea how long it takes to port a game to Switch.

Insinuating that other AAA games take just 9 months is just plain wrong. In fact, I'd argue Diablo 3 of all AAA games is one of the if not the easiest to port to the Switch.

Depends on the team size. It is a game that runs on systems that came out 2 generations before the Switch though so probably simpler to port.

Team was definitely much smaller than it was for original game, also again, its not same porting game that has smaller content and game that has big ass content. Also were you get 2 generations ago, game come out on PS3/360 in 2013. so we talking about last gen.

We have idea, generaly we can say it takes less than one year, and examples we have tells us it takes around 9 months, but of course that depends from team size, size and content of game, level of optimisation...

"Stilwell said that a team of “eight or nine” Blizzard staffers collaborated with Iron Galaxy, the studio that helped bring Skyrim to Switch last year."

So while hundreds developed the original game for years, ten people develop the port for months. This is why I always say porting takes so few resources it is nearly neglectable.

If you appoint "eight or nine Blizzard staffers" to do the job, yes.

Iron galaxy has 130 employees as of 2016.  We don't know how many people they used for the port but its that number + 9 Blizzard developers, so its well more than 10 unless Iron Galaxy had one person working on the game with blizzard.

Yeah, doubtful Iron Galaxy applied all 130 employees for this project. But let's say 20 or 30 worked on this port. Still a tenth of the original workforce, and made in lesser time too. My point that ports are extremely cheap compared to new games stands.