I am EWR based and very frequent user of the EWR Airtrain.

I personally would not chance the 40 minute connection to Amtrak at EWR.

The Air Train is anything but reliable right now. It is not running anywhere near the advertised 5 minute headways. (At best it feels like 10 minutes before 9pm where it runs like every 20)

Not to mention coming from UA either from Terminal A means a longer ride, or from certain UA gates at C a longer walk.

I mean being in F does mean you will be off the plane kind of quickly, but that of course assumes you have a good gate arrival ground experience. Also, far from guaranteed at UA.

I mean it is frankly embarrassing to write this, but I think the 40 minutes is almost a coin flip to actually making it.

Now when using NJ Transit this is less of an issue as the tickets are not for anyone train and at least on the NEC line it means that you have 30 minutes to wait if you watch the doors close in your face.

On Amtrak it means you are now ticketless and would need to rebuy a walk up fare.

So, what does that mean? Do you actually save time waiting the full hour and 40 minutes at EWR for the Amtrak train?

Maybe not...you could consider doing the "Trenton Shuffle". This way you are on unreserved trains and can simply take the next NJ Transit train that shows up. You can buy a ticket to 30th Street Station from the NJ Transit ticket vending machine at EWR.

You will get 2 tickets a NJ Transit ticket to Trenton that includes your AirTrain ride fee, and a second ticket for SEPTA that will get you to 30th Street. (You can also buy this ticket on your phone via the NJTransit App). Cost $29.50

At Trenton it is a cross platform transfer over to SEPTA for the trip to Philly. (Average connection time is around 20 minutes during a weekday.)

Total time from getting on NJT Transit to 30th Street is roughly 2 hours 15 minutes.

Overall travel time might be longer, but the flexibility and not waiting around at EWR might make up for that.

Just my 2 cents.