You have your appointment on the 20th and so should be fine to attend the seminar and receive your 'passport sticker' all at the same time.
I take it you already have a flight ticket for 21st?
Given all the factors that can cause delay it would probably have been safer to allow a couple of days extra in the plan especially for such a key requirement.
CFO does have a desk at the airport for emergency issue of the sticker on the day of depature but you need to book a slot with them so they can be sure to be at the desk. Worth considering if you face any issues