Zertifikat Deutsch

There's been enough dilly dallying on the language front, and it's high time I signed up for an expensive language exam as self-motivation to bring my German up to a respectable level. I checked the exam dates, and the next two options are the end of June or October! Since I don't know where I'll be in October, or what I'll have to do over the summer and early fall months, I think it's going to have to be June. They say that to be prepared for the test, a person needs between 350 and 650 hours of language instruction. I'm not sure how many I've had, but probably around 100, plus lots of exposure. What's a few hundred hours over almost 4 months, right?