When you're planning trips such as these down to the minute, one feels like you're on a timetable and you end up rushing things. Sometimes it's best to have a general idea and plan accordingly. Not that you are doing so, but plan on breaking from your itinerary some....
Asakusa and Ueno can be done in one day if you centralize your "targets". The area around Senso-Ji in Asakusa and the museum campus in Ueno. If you like going to museums, that'll add time to your stay there....
Akihabara can be done in half a day but it depends on how much you want to do there. If you're an anime fan you may want to go in and out of every store there, so plan accordingly. Sunday would be the best day to go there, preferably afternoon to evening so you see it in its full splendor of activity and lights.
As far as Shinjuku, Harajuku and Shibuya... it's best to start in Shinjuku and visit the TMG towers for the view.... then proceed east back to the station and the eastern part of the station, stopping by the discount camera and electronic places that rival Akiba in deals. Once you're done there in Shinjuku, take the Yamanote to Harajuku, get off , go to the right to cross the tracks to get to Yoyogi Park and the Meiji Shrine. Once you see that head back the way you came back to the station and cross the tracks once again to the station entrance and you'll run into Takeshita Dori. Take that to the Meiji Dori, hang a right and take it until you hit Omotesando. Take a left and go up to Aoyama Dori, then back down until you hit the little side streets on the left just prior to the old site of Kiddyland toy store... take those little streets down until you hit the Meiji Dori, which will take you to
Shibuya.... It's a nice walk and if the weather's good, so much better....
I wouldn't do Roppongi either.... though I haven't been there so I can't say if it's worth it.... there are so many places to see, you have to chose wisely and really savour and relish the ones you're in, because if you hit too many places, you feel rushed and don't enjoy them as much as you should....
Have these places in mind, along with a vague itinerary, with the plan that they can change in a moments notice.... If it's raining outside, then it wouldn't be a good day to go taking photos outside, etc. When I was there last, I had my Sunday reserved for Harajuku and Akiba, since I thought they would be where the action was. There was not a soul at the Harajuku Station cosplay area and this was past noon on a sunny 75 degree October day. I headed to Akiba after the Formula One race (I'm a fan).
If this is going to be your only trip to Japan in your life, then I'd cram as much as possible, but if it isn't, then plan to see what you missed, if it's worth it, on your next trip. My last one was the second tourist trip the Japan for me and while I saw more than the first one, I still missed many parts of Japan, which I plan to rectify in about 14 months....
I don't know what more to say, I am not even close to being anywhere near the vicinity of knowing my way around Tokyo, much less, Japan, so just take my advice as one person's observation, based on his own experience. Hope it helped a bit and, with the advice of others here, you can get a better picture of what's ahead for ya....
Just have fun and enjoy what you DO see and do.... Everything else will still be there for the next time you go!
And I apologize for the excessively long post....
