Here's some general advice on crafting a schedule to suit your writing style:
1) Don't be too ambitious. I agree with Ninja that three hours is a lot, particularly since you've never done a schedule before, so that is going to put you at a strong risk of burnout. My goal for the past three weeks has been 100 words daily, which is very low, but it's working out to an average of 844 daily, since the hard part is just getting started. So I strongly recommend under-setting your goal rather than over-setting it. The usual recommended starter's amount is 15 minutes, or 100 words if you're doing a word-count based goal.
2) Have a backup plan. If you're not meeting your goal, pick a smaller goal rather than giving up on it altogether.
3) Some people do better with time-based schedules, others prefer word-count-based ones. If you find yourself having difficulty committing to a set chunk of time, you might want to switch to a word count goal. Experiment with both and see what works best for you.
4) Know your writing moods. Do you have a specific time of day you write best during? Do you like to eat before or after eating/sleeping/exercising? Do you need to get your writing done before doing work/homework, or can you not focus on writing until you get other tasks done?
5) Count writing only. Brainstorming, editing, and researching is fun, but I recommend against counting it towards your daily writing goals. Too much brainstorming/researching/editing without writing to match it can suffocate your work.
6) Have a project in mind. If you're writing 3000 words a day, but each day you're writing "chapter one" of a new story, you're not getting anything done. Pick an idea you're excited enough about that you don't mind committing to it for the long haul. If you're not excited enough about your idea to write about it every day for months, you should be picking an idea that excites you more. (Unless you're writing short stories--then you can afford to be less focused.)
7) Keep track of your progress. Have a document where you write down how much time/how many words you do every day. Watching your progress accumulate is a big motivator.