This new update will be applied to both existing conversion actions and as well as the new ones which are currently set to the default conversion window.
A view-through conversion is a type of conversion tracking which provides you additional information about your display campaigns. When a user converts through a display or video ad, then that impression is viewable but cannot be clicked on.
With this change, the conversions that occur within one day of an ad impression will only be reported in AdWords in the View-through conversions (VTC) window. It will only affect VTC column reporting.
This shrinkage in default VTC window will make more sense for most of the advertisers.
Ben Wainberg, Manager of Display Marketing at Jet.com informs Google, “We’ve found ad views are more likely to lead to a purchase within one day, when our message is fresh in customers’ minds.”
In the Conversions column in AdWords, View-through conversions are not included. The last viewable video or display ad impression gets credit to be seen in default VTC only when the user has not interacted with that particular advertiser on other advertisements.
Even after March 29, 2017, advertisers will be able to customize the window setting for each conversion action from Conversions which are present under the Tools tab.