It would only "not matter" if the LHR-EWR-ORD flight was one flight number. If not then it doesn't matter if you are in EWR for less than or more than 24 hours.

As to the other question, I don't know, but my guess would be terminals in the same city (JFK/LGA/EWR) are considered the same "point of origin" with respect to the particular rule you are asking about. But more those knowledgeable will correct me - or someone who has actually done this.