They first performed in the Salzburg Festival in 1936, not 1938, as portrayed in the musical, and not as a ruse to give them more time to make their escape, as portrayed in the musical. The musical telescopes many events and a long time frame into fewer events and a very short space of time.
The musical simplifies events by condensing them into fewer occurrences within a very short timeframe. The actual event at the Salzburg Festival in 1936 is different from the musical's portrayal.