Hi,
It depends if it's a residence permit for the first time or a renewal of a residence permit.
Mine was 9 monthes for the first time.
For the renewal, it was about the same period to get the decision,in my case it was a negative decision then I made an appeal to the court of Helsinki and got a positive decision after 14 monthes of waiting,so the whole period for me to get renewed my work permit was almost 23 months in total! Wow!
My advice to you is just to live your life as normal and don't sit and think about the decision so much, just live your life and don't count the days and the months..etc..enjoy your life and enjoy every moment in it!
My regards and best wishes to all of you.