Can the imperial player wait until he sees who the rebel player commits to missions before assigning his leaders to missions or is it simultaneous?

So during advanced setup up does the imperial player place units first then rebel units or is it simultaneous?

Rebels assign leaders to missions first then the Imperials. Rebels cannot change their assignments once the Imperials place theirs.

In the Complete Setup appendix of the Rules Reference, 8.2 is Imperial unit setup and 8.3 Rebel unit setup, so that goes Imperial then Rebel.

Thanks so much