Under contract with ISP. How long do they get to fix my connection before I leave? Legally?

I have a 3 year contract with my ISP, but my internet is $89.00 monthly and about as fast as dialup even though it should be about 1 meg. I called them and they told me they would work on it next week so my question is how long do I legally have to give these people to fix it before I say you had your chance adios without fear of contract violation?