Swampland: My guess is now Friday. Otherwise they wouldn't have had to skip the Mid-Week sale since it usually only lasts until the weekend.
Though another possible theory is that they just forgot about the Mid-Week sale with the holiday and the long weekend ahead and the Summer sale will then start Monday?
Well, there were definately some weird things from GOG this week...
... the Kingdom Under Fire games went on sale without any explanation (not a part of the weekly sale)...
... there were two "flash deals" on Monday. If I'm not mistaken those were this week... and flash deals have previously been associated with larger sales...
... now no midweek sale...
(Wow, I need to get out more!)