sorry to ask a stupid question but when can i make an upgrade award booking?? im in the eligible fare classes and i've been trying to book an upgrade to business class for my flight online but it kept saying "Due to internal system error, you are unable to proceed further with this booking. Please close all open browser windows and try again."

can i only book an upgrade 48 hours before the flight?? cuz my flight is on the 12th and im trying to book an upgrade today.... so i was wondering if i have to wait till 48 hours before the flight...