Data point from recent YYZ-LGA trip, Canadian passport. Departed YYZ T1 mid-morning, maybe 10 people in Nexus security lane, breezed through in a few minutes. Only one other person using Nexus machines at US customs, again straight through in no time flat. Flight delayed, but that's another matter.

Return the following day late afternoon, YYZ T1 customs hall was an absolute circus, thankfully only 6 - 8 people using Nexus. Love the new machines that I don't have to squint into, was back in my car within 10 minutes. Main customs line looked to be at least 45 minutes or more. Baggage hall utter chaos, so gad for carry-on only.