Hello,
In this case, you need to use a business rule triggering After enabling a user account and your scheduled task will look like below.
Business rule
Scheduled task
In the rule action and task action/condition, you can use any of Adaxes custom date attributes (e.g. CustomAttribtueDate1) not used in other workflows. Pay attention, that the business rule will only work if users are re-enabled via Adaxes.