Conversation so far:
When did Lester Young join the Count Basie Orchestra?
Lester Young was with Count Basie for the first time in 1934.
How long did Lester Young stay a member of the Count Basie Orchestra?
Lester Young was with Count Basie for the first time in 1934, back in 1936, leaving in 1940, rejoining in 1943, and a reunion at the 1957 Newport Jazz Festival.

Question: When did he leave the band?
Self-contained rewrite: When did Lester Young leave the Count Basie Orchestra band?