What happens if I send a campaign through Journey Builder on a different date than the campaign Send Date in Engage?

Sent through Journey Builder before the planned Send Date

DESelect Engage has reserved a timeslot for the campaign, but for a later date than when you're actually sending it.

Hence, Engage will treat this like an unplanned campaign, meaning it will check if there are available slots the moment the contact is hitting the Engage journey builder activity. To make this decision, it will look at recent past campaigns, upcoming campaigns (and their priorities), and the applicable rules, and determine if the unplanned campaign can be sent today.

Sent through Journey Builder after the planned Send Date

DESelect Engage has reserved a timeslot for a campaign for the planned send date.

If the campaign is not being sent on the planned send date, the timeslot is reserved for 3 more days.

If the campaign is sent within 3 days, DESelect Engage's outcome will still be undersaturated for that campaign, unless another campaign comes into sight with a higher priority and there are not enough slots available to send both campaigns. 

If the campaign is sent after those 3 days, DESelect Engage will consider this an unplanned send and will check if there are available slots the moment the contact is hitting the DESelect Engage journey builder activity.