1 Paris: Isn't that backwards though? If our two-day trip is time dilated by a black hole, it'll still feel like two days to us. It'll only be weeks in the outside universe.
2 Spanners: Well normally, yes. But this is a negative black hole. Time dilation works the other way round.
3 Iki Piki: So, a white hole, then?
3 Spanners: No, a black hole made of negative mass.
3 Iki Piki: Negative mass?
4 Spanners: Yes. Hundreds of years ago people took sermons from fire and brimstone preachers and dumped them in a star. Bang! Negative mass black hole.

As rightly pointed out by several readers, the time dilation caused by passing through the intense gravitational field near a black hole might make the trip take longer as measured by someone in the outside universe, but to the people on board the ship the time still appears to pass normally, so the trip would still take a couple of days. Which is backwards from what Spanners said last time.

But this being science fiction, there's always an explanation.