You can show up a few times a month, etc. But the promise you make to God when you join the Church is to follow his will and dedicate whatever is asked to his plan.  
 
You will likely receive a calling as soon as you are confirmed a member, this calling will require a time commitment. Many Latter-day Saints spend an easy 15 to 20 hours a week between callings, assignments, and other Church responsibilities.  
 
If you are looking for a Church where a few hours on Sunday is your only commitment, the LDS Church is not the right Church for you. We are a Church of workers for the building of the Kingdom of Jesus Christ.

The LDS religion will show you the purpose of your life if you let it. But you shouldn't join the church unless you feel a burning in your heart that it is true. If you got in contact with the LDS missionaries in your area, they can answer more direct questions you may have. 
As for time commitment, a valiant church member who is strong in the faith usually attends church each Sunday, participates in ward activities and service projects as they come, attends the temple, prays and reads their scriptures, and serves in a calling. These things can add up. They aren't required, but people in our church do them because they want to.  
If you are genuinely interested in finding a purpose in your life, contact the missionaries. Then, if you feel that the church is true and it is something you want to be a part of, you have the opportunity to be baptized.