Bus takes about 10-15 minutes, depending on traffic. If traffic looks bad, they go the back way to avoid it

If you haven't already found it, the shuttle bus times are linked from the "Shuttle Bus" section on the left of this page. Book the night before to ensure a space, they run additional buses if needed / call in a taxi, but not last minute!

With GE, priority bag drop and a 10.40am flight, the 8.30am bus is doable if you have a moderate risk tolerance. 9.15am bus is too tight unless you really know what you're doing + have checked for any delays + have ensured there aren't too many other planes leaving at the same time. As a then non-GE but in business, I've done 90 minutes from airport to departure without issue but with no time for lounge / no time for anything to go wrong!