People in the Middle Ages basically slept when it was dark. They had no electricity, and lamps, and candles are actually very expensive things to use. In the movies, we always see torches, but, they only burn for about 20 minutes before needing replacing.
As it is fairly light at this time of year well into the evening, he might have been working - on guard for a feudal superior for example, or, checking on things in his own manor/castle. But, he would likely be going to bed pretty soon.