To change price validity period of pricing quotation, follow these steps:
Go to Admin portal, and navigate to the lefthand panel.
Therein, select Preferences and Settings dropdown menu, and then click on Preferences.
Navigate to Pricing Quotation Preferences, and open that dropdown menu.
To specify the price validity period, navigate to the row titled Price Validity Period (Days), select the Edit icon against that row, specify the period in terms of number of days into the window that opens and select Update to save changes.
Go back to Design portal, create a new design, and generate your pricing. The changes would be applied.