Originally Posted by
Steve M
Hyperdia seems to think that a 10-minute Shinkansen-Shinkansen connection at Tokyo Station is valid, so I'd go with that.
Hyperdia also thinks you can transfer from Seibu to Marunouchi line in 4min at Ikebukuro, and from Toyoko to Shonan-Shinjuku Line in 11min at Musashi Kosugi. Those are really minimum transfer times for folks who know their way around and assume you don't get lost or need elevators, etc. So I would not just assume that Hyperdia's connection times will work for everyone, especially if it's a big station and you're not used to the station or if you've got luggage.
That said, I think 10min will work for the OP's transfer.