GetSpellCooldown() does not work for Lay on Hands spell ID 471195 as ret with talent Healing Hands spell ID 326734 and when on cd always returns 420 for duration left.
This hasn’t been checked without the talent or as other specialisations.
The function you are mentioning is from the in-game API, not the web API.
This forum is for the Web API. For help with that you need to go to this forum instead.