Bart do you think that's a phenomenon that will get rid of what I'm seeing? If they are just noise specs, I can live with that since there aren't too many. The reason I have it set to auto is that unless I'm shooting really long exposures at night--which get noisy--I'd rather trade the time for a few hot pixels that I can fix pretty fast.
If the bright/hot pixels are caused (which is likely at 20 seconds) by the long exposure, then a darkframe subtraction should be able to reduce or eliminate them. In principle all systematic sensor non-uniformity can be removed with a darkframe. If time on location is an issue, you could try shooting separate darkframes (body cap on, same exposure time and ambient temperature, viewfinder closed) at a different moment, and then use a Raw converter like RawTherapee which allows to do darkframe subtraction as an additional processing step.
It is also possible that you have a sensor calibration issue, but that would also show on normal exposures, so based on your description that doesn't seem to be the issue here.