I can't afford to play that sumo game hover interesting it is, I have a lot of study to do but I find Sumo a good way to de-stress!
There are many sumo games to play! I am sure that at least one or two would appeal to you, and fit in with your study schedule. Most of the regular posters here play several of them. Try starting with http://isp.sumogames.com/ (the oldest running game, I think) - that takes only a couple of seconds to play each day during a basho (oops, make that about 10 seconds, as you also need to log in). So, as there are 6 basho a year, and 15 days to each basho, you would need 900 seconds or 15 minutes in total of your life, to play this game for a whole year.
Also, if you really want to understand about promotions / demotions in sumo etc, try out Moti's (Kintamayama) excellent post-basho game, 'Guess the Banzuke'... http://www.dichne.com/Guess.htm