Summoners Armor lasts 30 seconds, but very frequently the timer will end early.
The visual and buffs the ability gives still persist, but the timer is removed from the bar, leading to overcasting or having to repeatedly check for the visual effect of Bone Armor to fall off, which can be tricky in hectic pvp situations.
I have observed the timer ending prematurely in all these situations, and am unable to pinpoint the cause:
Timer ends immediately after casting.
Timer ends on barswap.
Timer ends on casting the skill Resolving Vigor.
Timer ends at 20 seconds as opposed to 30.
…………..
I have also observed Skeletal Arcanists timer to disappear when recasting, unsure if that’s related.