True, most of them run early in the morning and some in the PM rush hour. If there’s no issues w/ tracks/other trains, the trip from Metropark (Iselin) to Newark Penn Station is ~20 minutes on NJ Transit’s NEC route, no extra stops. It’s around 30 minutes for the normal Northeast Corridor route. Some Amtrak routes can do it in 10-15 minutes, but really saving time is almost negligible for a distance like this. You’d notice it more if you took a Amtrak route from Trenton-Newark Penn: 35 minutes (or 30 w/ Acela) vs 75 minutes (or ~50 minutes for express) w/ NJ transit, or even further outside the state like the service was intended.

Also, it’s not like you’re going to magically save time by taking an express/“high speed” train 14,6 miles. As of now (11:20AM, Christmas), you could book a ticket for Tuesday 27 December on Acela for either 95$ or 74$ (one left), and the other Amtrak routes for 83$. Meanwhile NJ Transit’s ticket costs 6,50$ to achieve basically the same thing from Metropark-Newark Penn, sometimes w/ express or local.