How to control how Iong I play with my clingy nephew?

My 6-year-old nephew, who is an only child with busy parents, always wants my attention almost every time he stays the night at our house. He always makes me play his video games (especially Minecraft, which I'm Really bored of btw) with him. If I refuse to play with him, he tells my mother to persuade me, which she does reguardless of whether I have school or other important stuff to do which Really pisses me off. If I don't play, he'll get upset and I'll get in trouble. Are you motherfuckin' kidding? I had to go to ******* summer school every year throughout high school because I spent the time I could've used to do my schoolwork on ******* Minecraft! Mom complains about how I don't spend enough time with him. I don't know what the hell she is talking about! When I do play with him, I get almost no time to myself and I end up playing with him for the rest of the time he is here. It can get VERY ridiculous. One time I even played with him for the rest of the day. If I want to play a game that I want to play (e.g. A JRPG), he will NOT leave me alone and let me play it. When I try to convince my sister to play with him, even when I'm trying to catch up with my schoolwork, she refuses. I tried to set a timer for 20 minutes, but he just kept on making me extend it until it turned into 2 hours! Call me an asshole all you want, but I can't just spend every last second of my time with him. I'm not his father! I'm going to college pretty soon and I can't be dealing with this ****.