Can I use it now and encounter themes pets from this or any other event? Or does it have to be used during certain events only, yes I have access to the list give to use it.

*facepalm* Thought you meant something else.

In LG, you can only encounter specific LG pets, nothing else, since that's what I remembered.

Most of the themed pets that you can encounter (don't know if they are updated or not):

https://www.sylestia.com/forums/?thread=63071
https://www.sylestia.com/forums/?thread=78521
https://www.sylestia.com/forums/?thread=100245

also, there aren't any themes from this event that can be found wild in the Lost Grove (though it has happened occasionally, for example, the blazing fireworks last year, and the two special aeridini themes from two years ago).
Currently it is only the lost grove's usual themes that are there, which are there all the time, regardless of any events or fests going on.
(Maeve can drop theme-containing boxes, and other wandering event bosses for other events can drop those or egglings depending on event specifics, but perfumes don't affect those encounters or their drops at all)

Lost grove perfumes work only in the lost grove, only affect the Grove encounter rate, and only count down when you specifically encounter wild sylesti in the Grove

for the four seasonal festivals, in the respective seasonal fest zones, you need a regular non-lg perfume, which itself only affects/counts down when you encounter enemies in that zone.

Thank you for the help