It is~when~

Archaeologists have divided the culture into five phases, corresponding with the late stage of the http://en.wikipedia.org/wiki/Longshan_culture, the early, middle and late stages of the http://en.wikipedia.org/wiki/Erlitou_culture and the early stage of the http://en.wikipedia.org/wiki/Erligang_culture. The early phase of the culture was influenced by the http://en.wikipedia.org/wiki/Longshan_culture, while the middle phases were influenced by the http://en.wikipedia.org/wiki/Qijia_culture; it was during this time frame when bronze artefacts begin to appear in the material culture. At this point Zhukaigou people were agriculturalists, with millet as a main staple, they also had sheep, pigs, and cattle.^{http://en.wikipedia.org/wiki/Zhukaigou_culture#cite_note-5}

I'd like to know if the underlined sentence is the variation of the emphatic expression "it is~that~."
Thank you in advance for your help.