Does the timing of a game release affect sales?

I know that in Game Dev Story, the time you release your game can have a noticeable affect on sales (ex. early December). The in game hints and tutorials don't mention timing releases at all.

Does releasing games at a certain time increase or decrease sales?

Yes, A little bit, if you get a booth in G3 while making a game, your hype and more fans can't wait to buy the game, so it is a slight increase, but timing does help, but marketing works more. As you get more fans you will generate hype just by developing a game, with the hype slowly developing over the course of development.