I would advise you to put the flights on "hold" just after midnight and that effectively gives you a locked in price for almost 48 hours. Check and re-check to see if revenue management releases more seats at the cheap price. With any luck the price will come down and you can cancel the hold and purchase the new fare.

Airline fares change at a moments notice. Fares generally are updated pretty significantly on Tuesdays but there are never any tried and true methods when you are waiting and hoping the price will go down.

Good luck