Yes it can be easily done
[QUOTE=AMHobbyist;3056334]Since I got no response to original post I am reposting. Hopefully I might get some comment even if only that my idea is unworkable and I should forget about it.[/QUOTE]
[QUOTE=Vendelo;3056406]Not realistic due to time constraints. I've been to Tokyo five-six times with Haneda and Narita experience.[/QUOTE]Several people have posted similar queries in recent years, I don't know if any of the have actually gone through with attempting it or posted their experiences. I hope you will be the first!
Personally, if I had a 6. 5 hour Haneda layover during the day, I would go for it. The biggest unknowable variable is how long immigration / customs would take. If it ends up taking longer than is workable, you can always just scrap the soapland trip and get some sushi / ramen and chalk it up to bad luck. But the soaps of Kawasaki are under 30 minutes from Haneda by train, less if you spring for a taxi. KiraKira in Yokohama is under 40 minutes. If you get through customs quickly and race over, you can then figure out how long of a session you can have.
The other layover scenario you mentioned -- 12.5 hour overnight -- wouldn't work for a soapland but would easily work for a delivery health in Tokyo or Yokohama. Heck, you would have enough time to go into Shinjuku and check into a cheap APA hotel near Kabukicho, hit up an oppai pub to get warmed up, and then get a delivery health girl, and you could squeeze in one or two late night / overnight meals while you're at it. There would even be enough time to grab a few hours of sleep before you have to head back to Haneda. I hope you go for it and then report back on how it went.