It looks like Valve is about to kick off its annual Steam Summer Sale, with SteamDB developer Pavel Djundik tweeting out that the Steam Summer Sale will begin on June 25.
Djundik tweeted that "Chinese sources are saying the Steam summer sale starts on June 25", clarifying that these sources are "generally trustworthy, but not fully confirmed". He followed up that tweet with another, tweeting: "Confirmed now, Jun 25 to Jul 9".
But then Avi Thour just came out and gave exact times, tweeting "CONFIRMED! The 2020 Summer #Steam Sale runs from 25th June @ 9:55 A.M. Pacific to 9th July @ 10:00 A.M. Pacific. Hold your money boys!"
So I guess there you have it -- June 25 at 9:55AM PST (I'd say more like 10AM) through to July 9 at 10AM PST.