Indeed, your sketch has intrigued me.  I love to hear more about the unexplained arcane devices with which JKR has casually endowed her characters.  You have brought the clocks to a kind of startling life and usefulness in the Headmaster's hidden chamber, and your analysis of Severus Snape's relationship with his two Masters is equally thought-provoking. 

Snippets that gave the piece real life for me:

--the shape of the room and its meager contents--except for the clocks, of course,

--the differences among the clocks,

 --the untouched lemon drops and their reason for being there,

--the word perii on the trunk,

Thanks for a delightful read!