In the world I am designing, the days last 9 years. The main problem I had was how life could have evolved on a world like this. An easy solution is to have the world start having 9 year days after life already evolved. I plan on doing this by having a rouge planet pass by, slowing the day length. Is this idea realistic? If not, what else could cause the planets day/night cycle to increase?

In the world I am designing, the days last 9 years. The main problem I had was how life could have evolved on a world like this. An easy solution is to have the world start having 9 year days after life already evolved. I plan on doing this by having a rogue planet pass by, slowing the day length. Is this idea realistic? If not, what else could cause the planet's day/night cycle to increase?