Originally Posted by
mmxbreaks
It'll take an hour to get into London and and hour to get back
And that's just the journey time: Piccadilly Line trains to/from T5 are every 10 minutes, and waiting up to 20 minutes isn't exactly unknown (I get that about once a month).
4.5 hours isn't really long enough to do anything but take the train into central London, take a selfie at Piccadilly Circus, turn around and go back again.