What Skyking said is the response I also received.
When I continued to press for answers on a local level, the further explanation was that passage of time is not always specifically detailed in the Bible... that the ones in the referenced scriptures did study and learn and prove their faithfulness, but the amount of time it took was not detailed (sort of reminded me of hitting fast forward, lol). And that the ones doing the baptizing were special appointees of Jesus and Jehovah, therefore qualified to make the decision on whether one was "ready" for baptism. So that makes the shepherds of the WTS the ones who, in modern day, determine one's "readiness" and "qualification" for baptism.
Please note that this is not necessarily my opinion or interpretation ... it's how it was explained to me when I asked for help researching and understanding the same scriptures you've presented. I too, would like to hear an honest Scriptural explanation from a sincere active Witness.
Willow