If one were at the I-278/I-478 jct at say 9 a.m. on the Thursday after Labor Day, what would the traffic be like to follow I-278 to I-87 to head across Tappan Zee and further up the NYS Thruway?
Not horrible, particularly since you're going off-peak direction on I-87 (traffic does drop off noticeably around 9-10am on weekdays, even in peak direction). But be aware that there's construction to rehabilitate the I-87 viaduct around Yankee Stadium, and the BQE can be problematic any time without warning, often at the Kosciusko Bridge.
Once you're past the Cross County you'll have smooth sailing the rest of the way up (barring unforeseen issues at the Tappan Zee).
Hopefully, they'll have the Tappan Zee fully open by then from the crane collapse. :D
Thanks for the advice on this...