Normally Ticket Price increases always go into effect on a Sunday. The earliest Disney will usually announce the increases is late on a Friday afternoon.
The only people who know in advance are some managers and high level people, the programmers for the ticketing computers, and the people who make signs and printed materials.
Often many of us who sell tickets find out when we come in and find that the prices on our terminals are changed, and the sheets we have in the booths to show Guests their choices are new.