If a user is very engaged with your brand and they are interacting with your emails and website frequently, they may have a smaller window between each email send from Cortex. Our models pick up on high engagement and know that more frequent sends will be optimal for conversions.
If you want to have more control over the time between Cortex sends (with the exception of Acquisition, User Triggered and Item Triggered stages) you can change the Cortex Minimum Interval to a specific amount of days. The Cortex Minimum Interval is a setting that allows you to adjust the minimum interval day for users in cortex between sends. More info here on this feature.