Oscar says that the 24 hours is almost up, yet in a later scene as Steve boards the sub, one of the mercs remarks that there are 14 hours to go.
The sub is shown sitting on the bottom of the sea in several shots during a good part of the movie, and it never gets underway afterwards, so it could not be suspended at mid-depth as it is seen in later shots, nor could it sink after the captain sets off the scuttling charges.
In the first shot of the sub moving past the camera underwater, the sub is moving much too fast for the slowly-rotating prop to be pushing it.