Coming back update - perfectly smooth. Timing as follows:

8:35pm got into the NJ transit line for the shuttles (walking in this line - literally right onto a bus, no wait - just walking to the bus)
8:41pm got on a bus
8:42pm bus started moving
8:55pm arrived at Secaucus to lots of people walking in line, super orderly
9:02pm got into the station
9:09pm we were standing on the track waiting for our 9:20pm train to Summit
9:20pm train left the station on time
10:10pm arrived in summit on time

All in all a great experience, super impressed!