Southwest is again making some schedule modifications and allowing changes to your itinerary, per Southwest T&C, at no change in fare, but subject to availability. Flights now affected are in March and April.
Southwest emails are starting to be sent tonight. Changes must be made within three days of notice. However, I suggest being proactive in checking your flights and not waiting for an email that may or may not ever come.
Reminder-even if your upcoming flight has not been changed, but the banner comes up when selecting to change, you can still take advantage and modify to a different date or flight, within a 30 day window, and subject to availability.