he passage of time is unnoticed by it as it appears and disappears at random but its existence will soon change. The rift was only the size of a sewing pin but then it materializes in the event horizon of a singularity (a black hole). It can't really be destroyed but it can be altered if conditionjs are extreme enough. It becomes curved in upon itself as it forms a Möbius Strip and begins accreting matter colliding with it. When it collides with the black hole, the explosion causes it to wink out of existence...
...only to appear somewhere else but it is now of a relatively huge size (around five centimeters of #2 pencil) and has gained its own gravity well.
It takes time for it to determine the boundaries of where it finds itself but it overcomes every obstacle in its way. It is unable to escape from the elevator shaft but it takes over the shaft, the elevator devices connected to it and all other accesses into the structure where it resides. There will be little warning as the thirty plus floors of luxury and bureaucracy become a scene of cross dimensional and cross time hell.