ITD and FTD were union contract 'arbitrary' payments. Train crews got paid by the mile not by the hour. So the railroad company had no incentive to get you out of a terminal, over the road, and into a terminal to tie up. They just didn't care. You could sit for HOURS with no additional pay were it not for ITD/FTD.
Where I worked (Sheridan WY) ITD started at 1 hour and 15 minutes after you were On Duty if you had not departed the initial terminal by that time. You got no extra pay for that 1:15 delay but went on "straight time minutes' from 1:15 until actually departing. Often you would get HOURS of ITD if the call On Duty time was off or the train had gotten delayed before it got to your terminal or if the yard (at Laurel) did not have your train switched & ready.
FTD gave the RR company 30 minutes from your arrival at the Final Terminal to get your train into the yard and get you tied up (Off Duty). If it took longer than 30 minutes th
en you got paid FTD. Unlike ITD, FTD _was_ retroactive to your arrival time. In other words if it took them 30 minutes or less to get you tied up you got no FTD pay but if it took them 31 minutes to get you tied up then you got 31 minutes FTD pay. Once on FTD you stayed on it getting paid 'straight time' minute by minute until you were tied up. If the yard was jammed you could make HOURS of FTD pay waiting to yard your train