Aspect of a fairy tale: Once upon a time

The aspect I have decided to focus on is the 'once upon a time' concept. I find this particularly intriguing about fairy tales as this opening does not specify a place, time or era. This seems to add to the mysterious and magical themes in a fairy tale- something that is vital for a story.
Every original fairy tale begins with 'once upon a time' which is a comfort for listeners, as it assures them (usually young children) that the demons and witches within the tales are no where near them so cannot harm them, yet they are close enough to learn the stories morals. The distance set between the children and the tales is important as if it were too realistic, or set in current times, the story would have less magical value and therefore be less entertaining.
The opening adds ambiguity to the fairy tale, which helps create suspense and tension within the story. This is important because like any story, a fairy tale needs a good plot.

Bluebeard

Bluebeard is wealthy, however feared because of his ugly, blue beard. He's been married several times, but no one knows what became of his wives. Therefore he's avoided by the local girls. Eventually he persuades the youngest of a friends family to marry him. After the wedding ceremony she lives with him in his grande château. 

Bluebeard announces that he must leave the country for a while, so leaves all the keys of their house to his wife, telling her they open the doors to rooms which contain his treasures. He gives her the key to one small room beneath the castle, stressing to her that she must not enter this room. She vows she will never enter. He then goes away and leaves the house in her hands. Immediately she is overcome with the desire to see what the forbidden room holds, and takes the key to the room.

Its floor is awash with blood, and the murdered bodies of her husband's former wives hang from hooks on the walls. She drops the key into the pool of blood and flees the room, but the blood staining the key will not wash off. She reveals her husband's secret to her sister Anne, and both plan to flee the castle the next day. But Bluebeard returns home the next morning, and, noticing the blood on the key, immediately knows his wife has broken her vow. He threatens to behead her on the spot, but allows her 45 minutes to say her prayers. She locks herself in the tower with Anne. While Bluebeard, tries to break down the door, the sisters wait for their two brothers to arrive. At the last moment, the brothers break into the castle, and as he attempts to flee, they kill him. He leaves no heirs but his wife, who inherits all his great fortune. She uses it for good.