Traditionally, the time to announce bad news is Friday. It is called a "Friday news dump" for a reason. If it is a real Friday news dump, they will wait until late afternoon/early evening so it misses the 6pm TV news.
Quite honestly, with the ongoing jury selection drama, the MSP city council approving a $27 million George Floyd settlement today, and the governor announcing on live TV that he will lessen statewide health restrictions, this afternoon would make total sense to announce the move. It would totally get lost in the shuffle.
I think leaving a coach in purgatory for an entire weekend when you know you're going to fire him is not better. But, there could be other reasons for waiting.