I was in Edinburgh in April this year and visited many of your sites. As I recall my timings:
People's Story Museum - I think I had only one hour before closing. I found it very interesting and would have liked 90 minutes - lots to read if you are interested.
Georgian House - Didn't visit, but it is not on the Royal Mile. Many of your attractions are and can be visited quite efficiently. I was delighted at how little time was spent going from spot to spot.
National Museum - This could take all day. I have written elsewhere that my visit was disappointing. Even as a visitor to many museums on many continents, I had trouble making sense of this one. I gave up after a couple hours when I'd planned to spend 1/2 to a full day. I found the organization rather random, especially in the historic exhibits I'd hoped to explore more fully. I do hope to try again sometime, but am not sure how I can better prepare.
Holyrood House - Palace probably 45 minutes to an hour. There is a good audio guide. I also wandered outside for another 30 or so minutes - many don't do this.
St Giles Cathedral - 30 - 45 minutes (or less or more depending on interest and if one joins a tour).
Gladstone's Land - I was disappointed here. There are attendant guides in each room. A person had to work hard when I was there to elicit information. Very little written info, just a printed brief guide that didn't much lend itself to informing a visitor. I was a solo traveler, maybe the attendants thought they'd done enough work explaining the rooms to the couples and family groups and that I should just listen to the tail ends of their presentations. In any case, I spent less than 30 minutes at a spot I'd expected to quite enjoy, but found wanting. The attendants did respond when asked direct questions.
Edinburgh Castle - Visited many years ago. I was disappointed then, I still remember specifics. When I looked at current reviews, I found the same reactions I recalled.