Its not "you cannot die" for 60 seconds, its just "if you reach 0 hp during this 60 seconds, the 10 second immortality begins" timer. the actual buff is still 10 seconds, it just auto activates at 0 hp while the 60 second buff is active.

And I usually press living dead when im around 10-20% hp. during big pulls I can lose potentially that remaining hp in less than a second.

however often times, i press it with a mere 15k HP left, and I end up never actually reaching 0 HP. healer heals, i get healed/shielded, etc, and my living dead simply doesnt activate and it goes on cooldown. I mitigate this problem by trying to press it as close as possible to dying, which can end up getting me killed because I waited too long.

Its just needlessly difficult to use in comparison to hallowed ground or something. in fact this same suggestion can be used for holmgang too.