This is definitely true, I expect that users will spend a bit less time on Facebook today. However, Facebook doesn't have a 100% fill rate of high value ads, s

This is definitely true, I expect that users will spend a bit less time on Facebook today. However, Facebook doesn't have a 100% fill rate of high value ads, so during the rest of the day they'll be showing somewhat more expensive ads to users, earning a higher average revenue. That will make up for some of the loss, despite lower usage.