Grumpy, like to go up and hit the sack by twelve latest (9)
I believe the answer is:
saturnine
But I can't explain it at all! Could you help me understand?
(Other definitions for saturnine that I've seen before include "dismal" , "may be brooding" , "Morose looking" , "offering little amusement" , "A rust nine chnage to be grave and gloomy" .)