What if I'm not a P? What if I'm a J instead?
In my case (not necessarily for anybody else), I wouldn't have such difficulty with the concept of 'time.' Time, to me, is an authoritarian's tool used to determine when I should end one activity and begin another. I can obey the authoritarian's tool until I get tired of it. As with Introverts losing energy when faced with the social realm, I also lose energy when faced with schedules and dead-lines. As Robert Pirsig would say, I confront a gumption trap.
For example, recently I have had to undergo physical therapy on my feet. This consists of - once a day of this, twice a day of that, and for such and such a time. Worse yet, I am left to my own devices, I don't go to any clinic because it is home-based therapy. I didn't have any problem scheduling time for this. But after a couple weeks I was getting tired of this, and began to backslide on the therapy partially based on my perception that I was making great progress.
I surmise that one difficulty is keeping track of time. I can't relax about time, I have to use Sensing and pay too much attention to how much time has gone by. My attention is divided, I feel distracted and annoyed. Over time, this becomes more and more intolerable.
On the other side of the same coin is my mental relationship with the concept of "space." This is harder to define. But in my experience, SJs (and SPs) have been much more relaxed than myself in their relationship with the world around them, while for me this has been problematic.