Hi all I'm new to the nex system
I try to take a photo of my car at night
using Bulb for over 10min
The photo was great but I'm not sure it is normal for the nex 7 to take like more than 10min processing the image
That's the long exposure noise reduction - it will basically take as long as the exposure time again to process. You can turn it off in the setup menu, which is fine if you shoot raw and use noise reduction in post but if you shoot jpeg only your images may be rather noisy. 10 minutes is a very long exposure though - where you taking pictures of a black car in a cave?
I usually shoot jpeg+raw and leave the noise reduction on unless I am shooting something like fireworks where I don't want to miss stuff while the camera is processing, but my 'long' exposures are usually 30 seconds or less with an occasional 1 or 2 minute one.
The camera is taking another 10 minute exposure, essentially an image of the back of the closed shutter. In a perfect world this would create a completely dark image, but in reality there will be hotspots on the sensor that were caused by it being active for so long and will show up as noise. These hotspots will be mapped in the second dark frame and subtracted from your first frame to reduce noise. The actual processing time is minimal.
As a test you could put a lenscap (or bodycap) on, place the camera in a dark environment and take a 10 minute exposure. The resulting file will show you how much noise is generated just by the sensor being active for so long. I think that this could be affected by temperature so the results may appear worse if you do this test indoors. A practical test would be to try two identical exposures with LENR turned on and then turned off, and see if you are still happy with the image that was taken with LENR turned off.