What's the minimum amount of time LIRR schedules between trains at Jamaica? Likewise for platforms at NYP, both AM peak drop offs and PM peak pick ups. And how about time between trains on each mainline track?
Just look at the timetable. Minimum times at Jamaica vary based on the move the train has to make through the interlocking and opposing moves at the time. Not a simple answer, but the schedules get fine-tuned when conflicts occur consistently and more time is added to certain schedules to compensate.
New York times vary also, depending on unloading/loading requirements. You can't have two trains unloading on 20 & 21 Track during the Commission Hours and expect a train to depart in two minutes. Departures on Tracks 18 & 19 can be made much more quickly. Moves from Line 4 to Track 17 must cross over and foul the entire plant. Generally, New York arrivals can be spaced as close as two minute intervals with some exceptions for departing and Amtrak conflicts.
Some parts of the Mainline can handle two minute headways though consideration must be given for station stops' effect on following traffic.