I want to set some thresholds on the start date and end date

If the # of days since the end date crosses the first threshold and case/task not completed, it marks the case/task as say "amber". It the # of days since the end date crosses the second threshold and case/task not completed, it marks the case/task as "red".

If something similar is can be done with start date in case case/task not even started, it is even better.

Of course, anything marked amber/red, ought to be escalated to the manager of the person assigned the task and informed by the system to the manager (or defined escalation point)

If real time is not possible, alternatively can reports be generated and sent out at scheduled times during the day.

Essential idea to have the system proactively inform about exceptions/delays to a approriately defined person rather than the person looking for exceptions in the system.