Given the other comments in this thread, this vote was very recent, with Sam apparently not knowing of the situation yesterday. They haven't even updated their website, this page still describes Sam as CEO: https://openai.com/our-structure
With this apparent rush, I'd habour the guess that the situation just happened to unfold on a Friday and wasn't planned as such.
There's a 1/7 chance it just happened to be a Friday; probably closer to 1/5, given that these things tend to happen on workdays.
I get that this looks like a strange coincidence, but major shareholders just had minutes of warning and they released the news before market close, sending Microsofts stock crashing down. Had they had the time to wait until Friday, they would have had 30 more minutes. So unless they had some fun with shorts, this doesn't look like a planned out action at all.
With this apparent rush, I'd habour the guess that the situation just happened to unfold on a Friday and wasn't planned as such.