Originally Posted by MegatopLover

Security lines vary a lot at T4 depending on time of day (worst in advance of the evening bank of flights to Europe), and also by whether you have TSA PreCheck and Clear. PreCheck plus Clear can clear security in 15 mins or less fairly reliably, unless something unusual is happening, even during the evening bank of flights to Europe. Non pre-check, non-priority, general Y pax, need to allow a good 45 mins to an hour to clear security during the evening departure bank. Two related reasons for that: pax mix skews to less PreCheck/Clear than usual US domestic departures because more departing pax are foreigners without PreCheck/Global Entry, so the PreCheck advantage is more pronounced. And because a disproportionately high number of departing pax aren’t familiar with US security screening procedures, more people get things wrong or are confused, so general lines move more slowly than usual.

If you’re outside the evening bank of flights to Europe, security clearance time can be a bit better. Completing checkin at 8:00ish for SQ 23 means going to security a little after 8:00, when the lines will be starting to ease.

My observations, FWIW. YMMV.