It's an interesting subject, the development of World time watches. The reason major manufacturers didn't produce true World Time watches before the 1930's was that worldwide standard time (proposed and adopted due to Sir Sandford Fleming efforts) wasn't adopted by the major countries of the world until 1929. There were a few specially commissioned "World Time" type pocket watches before this date, But Vacheron & Constantin were the first to offer a True World Time Watch in 1931 with a Loius Cottier designed movement.
This wasn't the first World Time though, Patek Philippe had used Cottiers design to produce a one off for Beszanger, a Swiss jeweller with his own shop. It is however rumoured that this watch used a movement supplied by V&C to Patek. What we do know is know that the Cottier family an V&C had a strong working relationship from early in the 20th century and were the driving force behind the adoption of World Time watches.