I told my airline I could be there August 1. I had 30 days vacation on the books. They called and asked if I could be there July 11 on short notice. When I asked the Skipper if I could go (using my vacation) he said, "You told me you'd stay until the end of July," and disapproved my leave request.
So, I stayed. Missed the July class and got assigned a class date in September. The silver lining was I used the 5 weeks off to move from coast to coast, driving two cars. Lost about 13 seniority numbers, but in the end it really didn't matter all that much.