Thanks to a tweet straight from the official Japanese Pokémon twitter account, we learned on the 2nd of June, we would get to hear more about Sun & Moon and although we still have no ideas as to what will be revealed, at least we know at what time to expect the information.
From the same account that told us about the forthcoming reveal in the first place, comes the information that the information is going to come out at 10PM in Japan (6AM Pacific Time & 2PM in the UK.)
— ポケモン公式ツイッター (@Pokemon_cojp) May 20, 2016
It is still not known how the information will be shared with us, and although a video like the last one we got, would be the preferred outcome, it could also just as easily be shared by the same twitter account that made mention of this reveal in the first place.
Source: Pokemon.cojp (Twitter)