We don't know, but it doesn't seem to be constant.
As you say, time clearly flows differently in the Black Lodge (or the "waiting room", perhaps; the difference between these two locations isn't entirely clear) and the real world.
Your examples show that time often seems to flow faster in the Lodge than outside. We don't know whether this time dilation is constant. (We might learn this in the ongoing third season, although by the four episodes I've seen so far, I kinda doubt it.)
One example which seems to imply that the time dilation is not constant is the disappearance and reappearance of FBI Agent Philip Jeffries. In the movie Fire Walk With Me, Jeffries suddenly appears in the Philadelphia FBI office two years after he mysteriously disappeared from Buenos Aires. He seems to have been in the Black Lodge (or the waiting room, or the room above the convenience store, or a similar place) for a very short amount of subjective time, while two years have passed in the real world since his disappearance. While we don't know how much time he spent in the other realm, it doesn't seem to have been much longer than Cooper or Briggs were there while much less time went by in the real world.
Another example is the fact that while Cooper has been trapped in the Black Lodge for 25 years, he has aged 25 years. How much subjective time his mind has experienced is of course up in the air, but his physical representation in the Lodge has aged normally while he's been in there. And that's not just because the real-life actor has aged 25 years between season 2 and season 3 out of universe, mind you: In the third season 1 episode, Cooper has a dream of the Black Lodge where he sees himself 25 years older!
We also know that the different flow of time in the Black Lodge is not restricted to simple time dilation.
In Fire Walk With Me, which takes place before the two seasons of the series, Laura enters the Black Lodge in her dreams. It's clearly not just a regular dream, as she communicates with entities there about things that we, the viewers who have seen seasons 1 and 2, know are true. In this dream, Dale Cooper is in the Lodge. She then "wakes up" in her dream to find a bloody Annie Blackburn next to her in her bed. Annie says that "the good Dale" is trapped in the Lodge and can't leave.
Of course, Annie's death and Cooper getting trapped in the Black Lodge doesn't happen until way later in the timeline, in the season 2 finale, and Fire Walk With Me takes place before season 1.