There is a wire that goes to the coil from distributor. A timed signal from that wire makes the coil to generate the spark voltage. The timing of that signal is varied by the fixed, centrifugal and vacuum advance. All are mechanical variables.
But if somehow a microprocessor based device is designed to just delay this signal in time, we will have a timing retard processor. Here i will mention that a timing advance processor will be impossible to design as you will not know when the signal will come. you never know the future, right?
I hope i made the point clear.