nope... mine has the exact same behaviors. She only will come out at night or when she thinks I'm not looking. Otherwise, she's in her log for the most part.
Your pleco's growth is not stunted, clowns only get to be about 3 to 4 inches long, so you have nothing to worry about in that regard.
I feed my clown an hour after the lights go out. I also turn off the surrounding lights so she's in complete darkness. When an hour's passed, all the other fish are resting and the pleco's out to play, that's when I feed her the algae wafers or pellets, whatever I happen to have on hand at the time.
So in short, your pleco's behavior is absolutely normal
