If I understand your requirement correctly, you have a series of events that you know will occur on fixed calendar dates and you are seeking to trigger a message to inform a designated person to perform a set task 'x' number of weeks prior to that event occurring.
If so and assuming you have a Microsoft Windows based system, you could use the Windows 'Task Scheduler' system to create a task for each desired event date.
How to go about creating a task and set a trigger, such as display a pop-up screen message or send an email to someone, there are some instructions available here:-
http://www.digitalcitizen.life/how-create-task-basic-task-wizard