@i-Norm There's two ways that will lock you in as the Jumpmaster:
1) Being the last one to choose, (and the other two didn't pick their legend before their selection timer had ended)
Note: The only way you won't be the Jumpmaster, is if you didn't pick your legend before your timer had ended, and one, (or both), of the other two players had picked a legend before their timer had ended.
2) Selecting a legend before your timer had ended, (even if you're the first or second one who gets to choose a legend)
Note: The only way this gets overridden, is if the second or third player also picks their legend before their timer had ended.