I'm thrilled to finally read about Rendaku (連濁) in my learning journey of Japanese, and to realise that ときどき is a simple example of this phenomenon!!
However, "少々" in 少々 お待ちください still remains as "しょうしょう" instead of "しょうじょう" (with tenten on the second "少")
a) Is there any specific reason why Rendaku is not applied in this case?
b) I read that the exceptions to Rendaku are sometimes due to unpredictability and also due to sound-words.