Hello Christopher. What you want to do will come standard in Moodle 2.0 released later this year but in the meantime there is an extra plug-in called Activity Locking if you do a search and it does the same sort of thing for Moodle 1.9 (The one I have tried is the Activity Locking course format, at the bottom of the page the link goes to)
Courses and course formats
Conditional release of topics.
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