Alert pattern to handle repetitive tasks

Context

I m actually developping an application in which people have tasks to make in a day. It's just like "wash the window, clean the floor" etc.. etc...

Each task has a recurrence, and needs to be done at least one time in this period.

Example :

Task 1 has to be done every 15 days. Actually, it's been 16 days that it has not been done. So an event should be emitted.

My client needs to be alerted when something hasn't been done , on a time event, with a proper manner

I know that cron tasks exist for this, I could run one at midnight everyday, and send a mail alert with this. But what if I need to be exactly 15 days ? seconds by seconds ?

I really need efficiency without running this kind of scripts every days.

Does it exist a better way ?