The hourglass named in the title of Link's highly-anticipated DS quest will come into play by keeping you alive in a cursed dungeon that constantly drains your health.
According to NEOGAF translations of the latest issue of Famitsu, Link will tackle the caverns of an underwater shrine which is under a curse that slowly drains his health while he's inside.
The only way to survive is to use the Phantom Hourglass, which protects you from the curse for a limited amount of time.
As you progress through the game you will set sail to explore islands marked on your sea chart to find "sands of time" which fill your hourglass and offer you extended protection from the deadly curse.
It sounds like an interesting quest from the usual dungeon-busting of the Zelda series. Phantom Hourglass is expected to hit Japanese stores next month and we'll bring you hands-on impressions.