Complex wait flow action - need help!

Hello, I attempted to begin a pretty complex wait flow in a dialog campaign. The concept of the wait flow is this:

28 + Days away from leads expected start date (12-31-2016) they receive and email

14-27 Days away from leads expected start date (12-31-2016) they receive and email

7-13 Days away from leads expected start date (12-31-2016) they receive and email

0-6 Days away from leads expected start date (12-31-2016) they receive and email

I tried using the logic that all leads entering the flow will get the 28+ Day email until Dec 5th 2016 (26 Days before start date) upon Dec 5th 2016 all leads will then get the 14-27 Day email and so on. However, if a lead is created via service API (the trigger for this campaign) on Dec 8th, they would start at the top of the flow getting the 28+ Day and 14-27 Day emails at the same time. I'm not sure how to create this wait flow to make it work for leads created by API or if it's even possible to do this.

-Jenn