What role does the cigarette play in the short story "Contents of the Dead Man's Pocket"?

In Jack Finney’s short story “Contents of a Dead Man’s Pocket,” the burning cigarette marks the passage of time. 
As Tom Benecke’s wife prepares to go out to the movies, he opens the window because he is feeling hot and a bit guilty about not accompanying her. The other notable action he takes is to light a cigarette, which he places in an ash tray on his desk. This action becomes significant as the plot progresses.
After the paper flies out the window and lands on the ledge, Tom’s adventures begin. The rising action describes the precision of his movements on the ledge, his fear, his attempts to garner attention, and ultimately, his ability to return to the apartment window. To both Tom and the reader, it seems he is on the ledge for a long time, but the sight of the burning cigarette changes that. When Tom returns to the window, a trail of smoke catches his eye. The cigarette is still burning in the ash tray. This indicates that Tom was on the ledge for less than the length of time it takes for a cigarette to burn. In those few minutes, Tom undergoes a life-changing experience.

A movement from his desk caught his eye and he saw that it was a thin curl of blue smoke; his cigarette, the ash long, was still burning in the ash tray where he'd left it—this was past all belief—only a few minutes before.