Originally Posted by
jackal
If you have an off-peak ticket, it's also not valid during the Friday and Sunday peak times, which are, IIRC, any departures from 10am-5:59pm.
The fact you have to book a specific train rather than a date is probably just a limitation of the reservation system. They really should just have you pick a date and ignore all of the train numbers, but reprogramming ARROW to accomplish that is probably not worth the expense.
I think (but am not positive) that the "peak" times are Fri/Sun from 9 a.m. until 7 p.m. The exact times are stated on the ticket so you won't need to guess. (It's strange that this distinction isn't noted on the timetable or, AFAICT, anywhere on Amtrak's website. The only place I've seen it is on the ticket itself.)
As far as booking the specific train, I agree that this is confusing for unreserved routes. IME most people on the unreserved section of the Keystones simply purchase a ticket at the window or use multi-ride tickets, both of which eliminate the need to specify which train they want to use it on.