This looks just extremely interesting. I'm wondering what kind of strategies this card could open up? I'd guess we'd see some 30 card decks with 6 hourglasses.
Keep 2 fire bolts and two rewinds, then draw cards like crazy? Or just any kind of cheap creature spam. Retrovirus anyone? Or Scarab to stay in almost mono-time? Or play a quinted creature, wait until you have 3 cards left and start spamming SoDs?
Long story short, I find this to be one of the most interesting ideas I've seen up to now, it perfectly fits time's theme... The only thing I'm really wondering about is balancing. I guess there are even stronger strategies then the ones I listed.
Edit: Endless nightmare just came into my mind.
Btw: Is eternal loop also copied into the bottom of your deck when you play it? I guess not, but I'd rather ask.