also can set up panic opens on monday, if one has guts of iron or OPM to use.
The market will drop on the next trading day, but I think the panic would be greater if the takeover was announded on a weekday. Doing the change over the weekend should cause less of a panic, allowing investors more time to analyze the situation.
Personally, I'm in favor of 24/7 trading, but under the current system, this takeover was best announced on Friday after trading closed.