As you have heard from the other folks, it is doable, but ambitious for Day 1. Frank and Kelly provided some good advice to play it by ear and see how you feel after the flight, avoiding pre-purchasing tickets if you are too tired gives you flexibility to rest if required. If you arrive at 6:40 a.m., you will need to clear immigration and get into the city which could take several hours, so you want to account for that in your timing if you do purchase tickets in advance.
I know for me, I don't sleep on the plane, but I still try to stay up to a local bedtime. In order to deal with that first day, if I can get into the hotel early, I get a shower, some breakfast and then get ready for the day. I try to pace my day with as much outdoor activities and walking as possible and to save both indoor activities and my must see attractions to the second day when I can appreciate them more. You will only know what works best for you once you try it.
Have a great trip,
Sandy