can a person taste the difference between coffee that has been ground 8 hours prior to brew vs 12 hours prior to brew?
While the timeframe between grind and brew affect the taste of the coffee I wouldn't go as far as measuring it down to hours. Of course it is best to grind directly before brewing, but in your case, as you use a timed drip maker I don't think it acutally does make that of a difference. 

Plus other aspects also affect the flavor of your coffee (water temperature, temperature of surroundings (kitchen), way of extraction (in your case it could be the way the grounds sit in filter) and, for a great deal, the age of the coffee itself. So if you taste a difference, it could be the result of (an)other factor(s) as well. Not only the + 4 hours of 'sitting time' the grounds had.

To sum it up: Simply try it yourself (as Pete Becker mentioned in the comment).