Since I don't have one at hand right now, could you tell me what this is about? Just for my insatiable curiosity 
If you are satisfied with the D5300 never being able to get a satellite fix, don't bother with the aGPS file. On the other hand, if you want the camera's GPS feature to be really functional, scuttle over to Nikon Europe or another of Nikon's sites and download the correct aGPS binary file for the camera. Put that file on a SD card and load the file through the camera's menu system.
Same procedure works with the AW1 and the independent GPS module for CX cameras, by the way. However, AW1 is less glacial than the D5300 even without the aGPS file. After updating the camera its GPS responds faster, though.