Need to know the maximum number days all the Notifications will be visible for employee

I searched an invoice dated 5th November and the notification was disappeared. I had searched this invoice within a timespan of 30 days.

So, I wanted to know what is the maximum number of days all the notifications stays in the BPM worklist for employee.

Note: In the task configuration, for invoice approval workflow task, deadline is assigned as "Do nothing".

Looking for some positive responses with justified statement.

Thanks & Regards,

Akanksha