It simply tells you that you can take 12 images before the buffer fills up and your camera will stop firing until enough data has been written to the card to free up space for another image.
Unless you take a lot of rapid-fire images, it's not something you need to concern yourself with. IFAIK, there's no way to turn it off.
Ok, it seems when doing say 2" or 3" exposure, (just an example), that because of R 12 its taking longer on exposure time ?
The buffer has no influence on shutter speed. It may be taking longer because you have "Long Exposure Noise Reduction" turned on. What the camera does then is take another 'image' at the same shutter speed, but it doesn't record an actual image as the shutter is closed at that point. It uses the data from the second 'image' do determine signal/noise ratio.
Unless you shoot rapid-fire like sports or wildlife, just ignore the readout.
It doesn't affect a thing. It only is an indication of how many more frames you can take before the buffer fills up and you will be forced to stop shooting. If you fire away like a machine gun, yes, you may have to stop or slow down. Especially if you shoot raw. But if you fire off frames in 4-6 shot bursts, or shoot JPEG only, it will never really be an issue.