Watch the prices at the dealer carefully.
Dealer stock is either free on the floor & pay for the replacements or on x months credit.
In the first case the price will only vary when the factory says so
In the second case the price will drop just before the dealer has to pay for the stock.
This will be mower specific so if they have 4 on the floor, each one could have been a different delivery so their interest free times will expire individually.
One of the big mower shops actually rings contractors when this is about to happen and offers them a "contractor only" special deal, limited stock & limited time