The biggest issue I see is the fact that gravitational time dilation is considerable on the surface of the Miller's planet, but not so much in the relatively close proximity of the planet, where the mothership is. I just don't get that part.
The explanation Kip Thorne offers in his book is that the lander ends up slingshotting around two things, like black holes and neutron stars, that happen to be in the right places to drop the lander into the gravity well and then accelerate it back into a stable orbit close to the planet. Of course, that kind of maneuver twice, on both the descent into Gargantua's gravity well and the return trip, is totally implausible... the idea that there are so many high gravitation objects orbiting Gargantua near the planet's orbit that you can pull it off on no particular schedule... but it might not be physically impossible.
Wouldn't that be yet another reason to avoid that planet like the plague? Even if they set up a colony there, at any time the planet could run into an orbiting black hole or neutron star, or get slingshotted by one of them into an unfavorable orbit or into Gargantua itself.
I figured the mothership was still orbiting the black hole, in a much wider orbit. They could rendezvous by matching orbits using pretty standard manoeuvres, it would just take more time than if it was moving in a similar orbit as the planet itself.
