Lyric discussion by Jargo 

Cover art for Hourglass lyrics by A Perfect Circle

Like the rest of the album this is likely entirely relating to the current political climate, and I believe climate is the exact message of this song.

I believe the sentinels the song refers to are the various climate agreements, Kyoto, Paris, Warsaw and Durban.

Smashing the hourglass but the countdown carrying on I believe is a reference to trying to hide the problem of global warming but even if you break the clock time still passes.