If you open the tab for the event (press F5 on your keyboard or right-click the crystallised chocolate fragments from the event), the bottom of the window states that the time left for the Avoiding Dental Catastrophe event is approximately 9 days and 3.5 hours at this time.
“Eragon looked back at him, confused. "I don't understand."
Of course you don't," said Brom impatiently. "That's why I'm teaching you and not the other way around.”