The way I understand it, the main compartment is usually held at ambient (saturation) pressure. The team can go in an out of the water instantly, with the entry lock for extra safety, but no pressure difference during a normal underwater stay.
When it's time for the team to go back up to the surface, they will slowly reduce the pressure in the main compartment over 17 hours for the team to decompress. When decompressed (like being on the surface), they enter the entry lock, pressure is increased to ambient pressure in a few minutes, then they exit the structure and go up to the surface. The exit would be like doing a ~10 minute dive from the surface to 16m and back up to the surface.