Control Macro With Times

I am looking for code that will start a macro by counting in seconds prior to an event according to it's due time.

Cell Value A4, A12 A20,( more could be added, depending on how many workers are present at the office at the time)

So if worker A is due to start a task at 1.00 pm, then 45 seconds prior to that event the worker can be notified.
( Cell Values A4 and D4 )

Then there are multiple tasks to be performed and each task is reminded in seconds after or before the set times the events ( Act) is due to start.
The code would keep checking every 1 minute for a new list of events between the hours of 9-5 (Variable)