A day passes, a heart is lost. Use your time wisely.

What is Lifetime?
Lifetime is a simple challenge data pack that does pretty much what it was stated above. One day passes, you lose a part of your max health by 2. The lower your max health, the more vulnerable you are. If your max health goes down to 0, you'll be force killed and become a spectator (unless you have like cheats enabled or something).

How many days do I have left to live?
When you start a new world with this data pack, you will have at least 10 days left to live, but there are a few ways for you to bring back your max health:
  - Drinking an Instalt Health II Potion brings back 3 hearts (6 hp)*
  - Eating an Enchanted Golden Apple brings back 7 hearts (14ph)
  - Using a Totem of Undying sets the max health to its max of 10 (20 hp)
    *Only drinking a Healing II Potion works, having the effect by a splash potion or tipped arrow, does not work.

Was this data pack conviniently made for Valentine's Day?
By the looks of it it would seem so (because hearts lol), but it was just a coincidence that I had the idea around this time.

Then what is the item in the icon supposed to be?
It's a heart-shaped clock, if you coudn't tell at first glance.

This data pack is made without the need for extraction