1) I have downloaded my Genealogy List
2) Sorted according to country.
3) Input the time differential.
4) Created Groups in gmail country-wise.
5) Send according to time of Affiliate country.
Suggestion:
With the new gmail InBox, one can schedule the send later feature per one's requirement.
Remember, you need to do the above steps only once. Then it is only a matter of adding on new sign-ups.