I'll be flying through Edinburgh next summer (on the way to the Faroe Islands) and will have a long (7 hour) layover in EDI. We will probably want to pop into town for a few hours (although we will also want to be absolutely certain that we get back to the airport in time for our onward flight).
We have been in Edinburgh before (and we will have a couple days to spend there on the way back) so we don't need to try and knock off major tourists sights (and I have flown through through EDI previously - going from Orkney to London - but never have come or gone to/from the airport). We will probably just want to wander the Royal Mile, have lunch, maybe do some shopping or light sightseeing. Basically, we would rather spend those hours enjoying Edinburgh instead of killing that time at the aiport (which I recall as being fairly easy but not huge or offering lots of entertainment for a full day).
I assume getting from the airport to the city center (and back) is fairly quick and easy. What's the best way to do that, and how long should one allow? (We will arrive at EDI around 8 am and our onward flight departs around 3:20 pm, on a Monday in early July.)