I loved the level design, very clever use of the mechanic to create interesting puzzles. I would suggest making it possible to revert the hourglass, because it's a pain having to restart the whole level if you fail. Also, I would suggest binding the hourglass activation to a key, to make it easier. For example pressing Enter to activate a near hourglass. Otherwise, it can feel like this puzzle game requires suddenly some platforming abilities from you. Like in the second level, stopping the second hourglass on the right time is difficult.
Overall, great entry, I really enjoyed it. Cool to see how different our ideas where with the same title :D