I think when you go inside the docking bay you leave the server and go somewhere else. It only becomes a problem at small stations where people are stupid and cannot be bothered to go inside the station to give others a chance to land
Nope the inside, even the hanger itself, is still the same instance. So you can watch another player enter the docking bay, land on a pad, go into the hanger, return to the surface, and take off - and the landing pad is occupied for the duration.
And it's not just players that hog it, either. NPC ships that land at pads and enter the hanger also occupy the pad for the duration, which is especially frustrating at outposts (especially when in a medium ship and there's only one pad - made all the more frustrating when a tiny Sidewinder then takes off from it).
NPC pad hogging is actually more of an issue as occiasionally they seem to get stuck. This appears to happen when a player is allotted a landing pad that an NPC is already sitting on. Hasn't happened to me for a while, but seen other players still complaining about it.
Point is, if a single pad offered multiple garages, and if you're then forced into the garage upon landing (so you can't sit on the surface) it would be less of an issue.
On a side note, I would also really like to see docking tubes added to the exterior of stations, especially outposts, to add an additional docking method that takes up less space (and obviously has no hanger). That way there wouldn't need to be a size restriction on stations any more, and since they have limited function (basically just access to refuelling and the market) ships are less likely to remain docked to them for long. You could even add a docked timer to this type to ensure it. FD appears to have added docking hatches to the models of most, if not all, of the player ships as well - so they've clearly already considered this to some degree.
Simply put, if you don't need to use the hanger it would be nice to have the option to dock in a different way that doesn't take up a landing pad for someone else that might need it.