SPOILER WARNING
To understand the plot structure (such that it is) in Interstellar, you have to start with the writer's desire for the emotional ending of the main character with his daughter, who is now old. Everything that happens in the movie is a really forced way to reach that outcome.
The whole watch time-travel thing was more of that illogical nonsense in service of that conclusion.
The time dilation to make all this happens just doesn't work that way. You have to get to a significant percentage of c before time dilation becomes really noticeable. For example, at 0.9c you're still only at ~2x time dilation [1].
The gravity effects of the black hole don't make sense either.
The "science" of Interstellar is no more realistic than Star Trek or Starship Troopers.
Possibly you’re confusing stellar mass black holes and super massive black holes?
Time dilation doesn’t only occur at high velocities, so your link focusing entirely on velocity is accurate, but I think not really relevant.
The physics was pretty reasonable for the time dilation. Possibly off by an order of magnitude or so, but not ridiculous on its face.
Except for the wormhole.
Could have stood to be a full hour shorter, though.
When I watched Inception for the first time I walked out of the theatre in love with that movie (and I still am), but, leaving Interstellar I felt confused and underwhelmed.
Perversely I think I was actually very overwhelmed by Interstellar because after seeing it many times in the almost a decade since it came out (oh my god how has it been 10 years) it's become one of my favorite films, but, there is just so much going on that it was difficult to connect with it on the first viewing.