Why is it on the 4th Sabbath of every October?

The first Creation Sabbath event was Oct 24, 2009. This had more to do with the year than the day of the event, as 2009 marked the 200th anniversary of the birth of Charles Darwin and the 150th anniversary of his book, The Origin of Species by Natural Selection. Nikolaus Satelmajer, associate secretary of the church's Ministerial Association organized the event. Initially there were no plans for this to become an annual event but successful participation and enthusiam has led to a yearly, global celebration of Creation Sabbath.

Read more here: https://www.ministrymagazine.org/archive/2009/07/god-our-creator