the time disparity between Romilly (orbiting Miller's Planet) and Cooper/Brand (on surface of Miller's Planet)

I don't understand why there was such disparity in time between the ship orbiting the water planet, and the people on the planet's surface. Essentially 2 hours on the planet was roughly the equivalent of 201,614 hours orbiting the planet.

Would simply being in a solar system orbiting a BH create this much of a variance?

If so, do these same rules not apply while in Gargantua's solar system relative to the Earth's solar system? It seems as though people on earth only age more rapidly when the crew is either on a planet and/or passing through a black hole, but not while they are in orbit.

Did Cooper's daughter grow old while he passed through the BH or was it during his time on Mann's planet? Or Both?