Enabling Cyber Missions immediately generates the mission for the current cycle: it appears in your employees' portal and runs until the last day of the month. Subsequent cycles then start on the 1st of each month.
The start-of-mission notification does not go out the second you enable missions: the notification cycle can take up to an hour to start.
Sending is then progressive: allow 30 minutes to 3 hours for all of your employees to be notified.
Two rules can delay delivery:
A message is only sent between 9 am and 6 pm in the employee's own time zone. Anyone outside that window when the send happens will receive their notification the following morning.
A status (annual leave, meeting) or the "Do not disturb" option pushes the send back by a few hours.
If you are launching an internal competition, enable missions ahead of your announcement, ideally first thing in the morning: that way you can check delivery before you communicate.