Not only is 537 BCE a secular date, but the WTS cannot prove that exiled Jews returned to Jerusalem in that year.
Also, they accept the secular date of 539 BCE for the end of Babylon's rule, but they do not accept the method used by their secular sources to arrive at that date.
Consider this: the Babylonians only exiled the upper echelon from Judah. The Babylonians left "the people of the land" to care for it. When the upper echelon came back, there was great dissention as the elite attempted to exert their influence over the people who had been left behind. The "people of the land" frustrated the attempt by the elite to rebuild the temple for 20 years, until Ezra was able to exert pressure on them. The worship of a single God YHWH was the practice of the urban elite. The "people of the land" (who did not write the Scriptures) worshiped other gods alongside YHWH, such as Asherah and Baal.
Doug