YA teens are teleported to deadly elf world for ten seconds in Earth, but in Elf land they must survive for 24 hours.

It's about Teens (I think over 16) that go through "the calling" or some other phrase. The teens randomly and suddenly disappear on earth and their clothes fall to the floor. Everyone in the room looks at a clock and counts for a specific amount of time (I think 10 seconds) until they teleport back, dead or alive. Very, very rare to return alive. When they return dead, they are usually magically mutilated to look like gross things like having one huge arm or 50 toes or resembling an animal. Once, a person returned as a crazy huge monster and attacked humans. The teens are teleported to a deadly elf world for 24 hours, even though it is just ten seconds on earth. It was figured out that the elves lived in a tiny underground world and that was why the time was different. All children are raised as warriors and take survival classes to try to survive when they are "called".

I'm pretty sure this book is called The Call and is by Peadar O Guilin!

Yes, it is!! Thank you so much. I've been searching for a while. It was one of my favorite books! Thanks again!

Touchstone: The Call

Looks like there is a sequel.