We will be flying from Stansted Airport to Edinburgh on Sunday October 8th at around 4:30pm. How early do we need to be at the airport? We are from the US if that makes a difference.
Which airline?
Your airline (and its website) should be telling you how far in advance you need to get to the airport.
A typical time would be minimum 30-60 minutes before departure, either at check-in or at the gate, but your airline should be telling you this.
Make sure you have done your check-in online and printed out your boarding card.
Where you are from is irrelevant.