@SageAdviceDnD warlock: do invocations require actions or casting time? or are they innate passives? activated by act of will? or always on?
— gareth jensen (@gj1492) March 20, 2015
I’d suggest to follow Master Rodney advice
http://www.sageadvice.eu/2015/02/24/eldritch-invocations/ so if is a spell I’ll use its Casting Time.