Writing copy is a time-consuming process. This is what I tell every client before we begin, but few believe me. However, here's a calculation you can do yourself to determine how long it will take you to create your copy.
# of Web pages x the time it takes you to write and edit one page = your required commitment.
If you have a 20 page website and it takes you on average 90 minutes to write and edit a page, you're looking at a time commitment of 30 hours. This on top of all the other work you're already doing just to pay the bills! Suddenly one month to create all your content doesn't seem like a lot of time.
Keep in mind that besides writing a compelling piece of copy and editing it, you also want to create a descriptive, keyword-rich title and appropriate headers, include links to other pages within (and outside your site) if appropriate, and finish off with a call to action. You'll probably also want to run the final product past a trusted friend or associate, and make further changes based on their input. (I.e., is too full of jargon or too focused on you, rather than the needs of your visitors.)
If it takes you less than 90 minutes to create this compelling piece of copy, you're either extremely gifted, or not nearly critical enough of your own work. (I'm sure it's the former.)