#It works when the DM calls for a check
The only relevant range is when you request to do an action and the DM calls for you to make a Wisdom(perception) check. Otherwise, there is no clear guideline because environmental or other issues may impact your ability to use it, and those are also up to the DM.
##The Lythari This rare subrace also doesn't seem to be a playable race for PCs. They aren't listed in the playable races and there is no stat block for them. Closest is just being a drow, but that's not quite the same thing as that rare subrace.