I flew YYZ to LGA on Sunday August 22nd around 10 AM. While the nexus security line was closed, there was separate security line for Business Class, and it was quite short. Maybe around 5 minutes, and was definitely much shorter than the the regular line, which looked to be maybe around 30 minutes. (I'm not sure of the exact criteria for the priority lane, I know Amex Platinum holders can use it, and I imagine *G should be able to use it as well but not certain)

The US customs line was much much longer for non-Americans (i.e. Canadians). It wasn't obvious how quickly it was moving, but it looked to be at least couple hours if not longer. The line for US passport/green card holders was much shorter, it took us maybe 20 minutes or so for us to get through.

Hope this info helps!