The 20-30 units is a too small quantity, imo, and surely will harm the one in the wrong time zones at the announcement moment.
I propose you to have the whole quantity divided on continents or time zones, and let them go only what is remaining unsold after a whole day run.
Also, don't accept multiple quantity orders from the same location.
Also, would be nice if you accept preorders in the day before, or even now, to have an idea about the interest.
Just some silly proposals to make people happy