Because the sun was setting in the West, behind him.
From the Old Took's parties, especially his fireworks and stories.
He saw the sun coming up. And it was coming up with the mountains behind him.
sunset..it getting dark
The key words here are "behind the mountain", not merely that the sun is setting. This is significant because until now Bilbo has no reason to believe he made it through the Misty Mountains; likely he doesn't even suspect that possibility. He probably feels a combination of surprise, fear, and relief -- fear because he is really in the wild now, far from civilization as he knows it. At least there is a possibility of relief too because he is on the side of the mountains where his companions were heading. Likely he hopes, although maybe does not expect, that they have managed to make it through the mountains as well.
While Bilbo was sitting and thinking, a thrush flew up with a snail. It was knocking the snail against a rock, and it prodded Bilbo to remember the riddle from the map.
they waited until durins day and a crack appeared
Because it explains to Bilbo why they want to retrieve the treasure stolen by Smaug. Also it proves that there really is a secret door (used by Thorin's father and grandfather.)
They saw a stairway leading to a door.
The Hobbit tells us that the door was green, with a brass knob in the middle.
At the unexpected party, Gandalf gives Thorin a map of the Lonely Mountain, which has information about a secret door and the key to the secret door.
While Bilbo was sitting and thinking, a thrush flew up with a snail. It was knocking the snail against a rock, and it prodded Bilbo to remember the riddle from the map.
They became trapped in the mountain because Bilbo felt danger outside so they came in ans closed the secret door
He makes a sign on Bilbo's door that the dwarves interpret to mean "burglar for hire", which brings them into Bilbo's house.
He scratches a secret sign on the door that advertises that an "Expert Burglar" lives here.
none
they waited until durins day and a crack appeared
Because it explains to Bilbo why they want to retrieve the treasure stolen by Smaug. Also it proves that there really is a secret door (used by Thorin's father and grandfather.)
the secret door is in coralines room
"The Secret Door" by Enid Blyton follows siblings Peggy and Mike who discover a hidden door in the garden that leads them to the enchanted land of Curley Green. In Curley Green, they have magical adventures and meet fantastical creatures, unraveling mysteries and outsmarting evil schemes along the way.
The duration of The Secret of the Iron Door is 1.15 hours.
The door turns visible on a specific full moon every so often. The riddle has something to do with the time the thrush cracks the snail. Bilbo hears the thrush crack the snail, and realizes that today is the day the door can be opened.