The time.h example in NTP for the ESP8266 including day light saving time (DST) without 3rd party library is a lot simpler and just as efficient than in Examples/ESP8266/NTP-TZ-DST.
But it is not clear to me how he sets the timezone:
#define MY_TZ "CET-1CEST,M3.5.0/02,M10.5.0/03"