Akin posted a record in Skill Bug Reports
[Rune Knight] Stone Hardskin - Buff doesn't refresh upon reuse
Observed at 5:26 of the video linked below that the Hagalaz Rune was able to refreshed before the previous one ended. Also included SS that shows the timer does not reset itself.
Skill Name: Stone Hardskin (Hagalaz Rune)
Job Name: Rune Knight