"Durin's Day is the start of the Dwarvish new year, it is the day when the last sun of autumn and the first moon of winter appear in the sky together." Thorin explained. 
"Then we [i]must[/i] reach the mountain before then!" Balin spoke urgently. "We'll have to be standing in exactly the right spot at exactly the right time, then and [i]only[/i] then can the door be opened!"

Elrond turned to look at the dwarves, an expression of stern disapproval in his features. "So this is your purpose, to enter the mountain."
"What of it?!" Thorin growled defensively, this elf had no right to tell them whether they could or could not reclaim their home.
"There are some who would not deem it wise." Elrond answered simply.
"Like you?" Thorin scoffed. He clearly wasn't going to take Elrond's warning seriously.