To clarify, it's 4 separate emails (long story) going out same day, ideally starting at same time, hitting in the correct time zones and suppressed against each other.
So far based upon my experiments, if I start the sends all at same time, the suppression filter does not always know who to suppress, since some leads are in wait step and not in the flow yet.
Goal is 1) suppress all emails against each other and 2) get to people in correct time zone
Here is example of flow step
Here is example of smart list filters (filter 8-9 deal with the suppression against other lists).
Also, since data is dirty, the flow step to send by region doesn't even catch everyone. There are leftovers who don't qualify for any of the segments b.c we were not able to assign them to one. So I don't know how to deal with that either.