We took the train to the Shinagawa Seaside Station - you'll want Exit C to come out in the Oval Garden.
(We ended up on the wrong train and went, well, we don't know where, it was way in the wrong area. Hopped out, got on one going the other way, started over again. The Osaki to Shinagawa Seaside is almost twice the price of Shinagawa to Tokyo Station - we can't figure this system out, it makes no sense!)
We're staying at the Sunroute Shinagawa Seaside, right at the "forest" in the east tower. We step outside to the Oval Garden, with the Aeon at the opposite end. On the right side (back to the Hotel Sunroute, facing the Aeon) is the Excelsior Cafe. Tea, coffee, etc.
Ten AM Saturday at the Excelsior? (Past the Tomato Cafe, which makes us laugh, and before the Vie de France, where we get a morning croissant.)
10 AM works for me. I suspect there's only one exit A.
Would it be easier to meet at a cafe here at the "forest"? The Excelsior Cafe is nice because the smoking room is closed off, so the cafe isn't all smoky the way some of the places can be. (I have asthma, so the non-smoky places really matter to me.)