The gravity from the black hole (BH) will have no effect on their ability to take off from the water planet itself. Objects in orbit feel weightless (think astronauts in the ISS). If you're only worried about getting off the water planet then there should be no problem.
However, if they were to try to put some distance between themselves and the BH then they'd find it a much more difficult task.
Assuming the BH isn't rotating very fast, the time dilation factor for a body in orbit relative to a stationary observer at infinity is:
$$\frac{d \tau}{dt} = \sqrt{1-\frac{3GM}{c^2 r}}$$
The escape velocity of a BH looks the same as it does in Newtonian mechanics:
$$v_0^2 = \frac{2GM}{r}$$
So if the mass of the BH is ~100 million solar masses, the radius at which the time dilation is 60,000 times normal is at $r \approx$ 275 million miles $\approx$ 3x average Earth-Sun distance. The event horizon itself is at $r \approx$ 2x the average Earth-Sun distance. Meanwhile the escape velocity at the planet radius is about 82% the speed of light, or $v_0 \approx$ 250 million meters/second.