At some point Facebook is going to have to take a stand on which one it is. Indefinitely or for the next two weeks.
It does not mean "permanently", though it's often used to imply that without saying it outright.
So in this case they're saying "anything from two weeks and up, with no decided end".
"we are extending the block we have placed on his Facebook and Instagram accounts for at least the next two weeks, but potentially longer."
They are laying some of their cards bare here, but what I find funny is that if the president doesn't use Twitter, Instagram or Facebook as the dominant way to promote their message, they're not under the thumb of those platforms either.
Just like ordinary people aren't under the influence of social medias manipulation (intentional or not) if they just don't use the platform. We all willingly hand over that power to the platforms.
(More seriously, they'll wait until the dust has settled; they're hedging against the possibility of the peaceful transition of power not happening)
1. Indefinitely: The date range has no end.
2. And for at least two weeks: The beginning of the date range is at least two weeks away.
From this, I conclude that Mr. Trump's account will be muted for at least two weeks, and thereafter it could be un-muted at any time, but possibly the heat death of the universe may make the whole thing moot at some point.
They are in a real sense permanently banning “President Trump”