If it's not listed it's almost always a standard action.
That happens to be the official ruling. Here's the text for you.
Unless otherwise noted, activating the power of a revelation is a standard action.
It can be a bit confusing if you read over that part. A lot of abilities don't name their action. Some I wouldn't consider a standard action at first glance myself.
Page 186 of the core rulebook:
Supernatural Abilities (Su): Using a supernatural
ability is usually a standard action (unless defined
otherwise by the ability’s description). Its use cannot be
disrupted, does not require concentration, and does not
provoke attacks of opportunity.