Scheduled notifications based on user departure date

Hello,

We need to send automated notifications related to user departures at specific intervals before their leaving date, for example:

• 20 days before the departure date

• 5 days before the departure date

We are currently using an object policy with the activation mode set to:

<activation>SCHEDULED</activation>

However, we are not able to define a fireTime dynamically based on the user’s departure date attribute.

Do you have any recommendations or best practices to implement this type of scheduled notification based on a date stored in an attribute?

Thank you in advance for your help.