Susie-Q's through trains, the SU-99 (westbound) and the SU-100 (eastbound), are predominately night trains.
I live just north of the Susie-Q mainline through Pompton Lakes and can hear them blowing for the various crossings through Pompton. The SU-99 usually comes through between 9pm and 11 pm. The SU-100 usually comes through between midnight and 6am. I just recently caught an SU-100 at the Wanaque Avenue crossing in Pompton, but that seems to be the exception rather than the rule. Both 99 and 100 will always call clear of Butler, so that can help you if you are chasing.
As for the locals, the locals run day or night as needed. I've noticed that the bulk transfer on the Pompton Industrial in Riverdale normally gets service at night, usually between 11pm and 1am.
I'm sure you have a scanner with the NYS&W Southern Division frequency programmed in it, as well as the frequency for the end-of-train devices. If not, here they are:
NYS&W Southern Division: 160.485 MHz.
End-of-train telemetry device: 457.9375 MHz.
NYS&W is a fairly busy railroad but you need to be a bit of a nightbird to
see all the action.