CiviCRM Rules - Condition for contacts created X days ago
You may be able to achieve this already out of the box.

Create a rule like this:


Trigger: Contact added to group.
Condition: Contact is in group "the one you want"
Action: the desired action, with 14 days delay. Then check the box for rechecking of conditions. (You may also want to have an action of removing contact from the original group, so that the condition is no longer met, somewhere down the line...)