I fly QX a lot. The boarding time listed on the Alaska app and on boarding passes is always 5-10 min. prior to when they really board. I think they default to the boarding time that Alaska uses for their 737's. Since a Q400 is smaller than a 737 it is quicker to board. Honestly I dont care what time they board as long as the depart on time.

As far as the flight being on time, that can be a toss up. Since QX aircraft do a number of flights a day, any delay anywhere during the day can cause issues all day and night long. That being said the app usually is good about updating delays.