If it is simply a visibility of the event on the front end you can set the access level for the event to Registered initially, then after 2 weeks change it to Public.
If this is something you want to do for all your events then you could set up a php script that monitors the published date of an event, and after 2 weeks changes the access level to Public. You would set up a cron task to do this that runs daily.
if this is for only some events then define a specific category for them and only check events assigned to that category.
All pretty easy with a little bit of php understanding and knowledge of the table elements involved.