For Edinburgh, I would start at the Castle and then walk the 'Royal Mile' to Holyrood Palace.
You will dock at Greenock for Glasgow - 3 principal choices dependent upon weather:
Take a nearby ferry to the Isle of Bute - for the Mount Stuart Estate - any foreign visitors I have taken there class it as a highlight and not a lot of people go there. A hidden gem.
Go to Glasgow if you are a CRM fan. Also some very good free museums if that is your thing. Also Glasgow has a HOHO bus.
Play a round of golf at one of the many local courses. Easily arranged in advance but be warned the courses are hilly
One last thought - Loch Lomond is not beyond reach either - plenty of time to climb Ben Lomond
PS The Queen's Diamond Jubilee celebrations are scheduled for beginning of June.