Here’s my first Casiotron, released in 1976. The R-17 X-1 was the first Casio with world time indication.
As far as i know, the first multifunction Casio with world time, stopwatch (only seconds), a counter (counts the number of times you press the button), time memory (records the time when you press a button). World time is limited to these 6 cities/time zones : Tokyo, San Francisco, Chicago, New York, London, Paris.
The module (17) was not made by Casio but by NEC (Nippon Electric Company, today : NEC Corporation) and was used in several watches like the R-17, S-14 and also the “Tissot Data Recorder”.