It depends if the automatic campaign has already been launched at the time of the change.
Two scenarios can happen:
- The campaign has been launched already: the new design will be updated daily only;
- The campaign has not been launched yet: the new design will be used on the current day or instance.
The reason for this behaviour are that:
- Automatic campaigns run only once per day at the hour scheduled.
- Trigger campaigns use a rolling send-out system and the message is reused for new recipients throughout the day as the conditions set within the filter are met.