> How do railroads determine when it's the time to write a new Employee Timetable and what is the proper procedure?

The timetable-special instructions contain details specific to each subdivision and how a specific Rule is applied on the subdivision. They are the repository of this information for the operating employees. As changes are instituted, they are posted in the form of train order, then timetable bulletin, and when these changes accumulate to a certain level, a new time table. Nowadays, this order is track bulletin, general order, then new timetable. By mid-1985, schedules became a thing of the past, so they no longer appear, although the station column still does.

> Do they have to submit the new timetable to FRA and wait for their approval?

No

> Do they have to reissue one every couple of years?

There is no set time period; see my first answer.

> It's more like Subdivision specific rules...

Correct.

> And directory for management...

You have to know who your supervisors are.