Welcome Drinks, for those getting in early, will be at the
Eau de Vie Lounge at Hyatt Regency Tokyo.
The Lounge is advertising a happy hour upto 20:00 (8PM), the dates for which, at present, only run to 31st March. I'll be keeping an eye on the relevant page and update this post once I know for sure if the Happy Hour has been extended to cover the 'do dates.
Given the number of people staying in the adjacent area (Hilton, Park Hyatt and a couple of other hotels are all a short walk away, as is the Shinjuku Station), the location works well.
The plan (or the semblance of one!) is to meet there around 19:00 for a beverage or few, and we'll definitely be there until 20:30; after which, depending on impromptu plans, we'll either head out to dinner (and more drinks), stay put or retire for the evening.
The beverage menu can be found
here