My bet is that she announces Monday the 18th. Beginning of the week and a news cycle. It's also the anniversary of Paul Revere's ride as well other significant dates.
Maybe in Madistan she'll hint about running to get the Sunday morning shows and then go full Monte Sarah on Monday.
Or maybe not.
She is outside the conventional box.
Suppose Guv Palin were to be speaking somewhere in Wisconsin, and call up the Alaska station - announcing simultaneously live and on the radio show...
Just saying. :)