The Hobbit: An Unexpected Journey2012

Elrond:
Stand by the grey stone when the thrush knocks, and the setting sun with the last light of Durin's Day will shine upon the key-hole.

Bilbo:
Durin's Day?

Gandalf:
It is the start of the Dwarves' new year when the last Moon of Autumn and the first Sun of Winter appear in the sky together.

Thorin:
This is ill news. Summer is passing, Durin's Day will soon be upon us.

Balin:
We still have time.

Bilbo:
Time for what?

Balin:
To find the entrance. We have to be standing in exactly the right spot, at exactly the right time. Then... and only then can the door be opened.

Elrond:
So this is your purpose? To enter the mountain?

Thorin:
What of it?

Elrond:
There are some who would not deem it wise.

Gandalf:
Who do you mean?

Elrond:
You are not the only guardian to stand watch over Middle-earth.