Here's where somebody actually did the math:

https://www.quora.com/In-Interstellar-movie-2014-how-close-exactly-is-Miller-planet-has-to-get-from-the-Gargantua-black-hole-distance-in-km-in-order-to-has-such-extreme-time-dilation-1-hour-equal-7-years-back-on-Earth-Need-accurate/answer/Bill-C-Riemers-1?ch=10&oid=395871518&share=b3c1ff02&srid=tze0&target_type=answer

TL;DR For such extreme time dilation, the planet would need to orbit just outside of photon sphere. There are no stable orbits that close to the event horizon; the planet would either fall into the black hole, or it'd be flung out into space.

The photon sphere is a sphere around the black hole where gravity is so extreme, photons are orbiting black hole in circles.

The black hole would need to be supermassive. Because anything smaller (e.g. solar mass black holes), the tidal forces that close to the event horizon would be so large, they'd shred the planet into tiny pieces... Or basically anything else, such as spaceship or a human.

For entire solar system to be so deep in the gravity well to experience time dilation as extreme as in the movie, and not be either destroyed or stripped of its planets, the black hole would need to be many orders of magnitude larger than anything we have ever observed. From what we know, no such black hole can exist. There was simply not enough time since Big Bang for any to grow that large, and due to the expansion of universe, no black hole will ever be able to grow to such a large size.