If you do not know the Envoy of Winter is a rare white stag. It is the only one with this skin, so Hunters are trying to tame it. Players can summon it by collecting Shiversnap Blossoms and throwing them into a pool. However, if you do summon it you are most likely not going to be able to tame it before player show up and kill it. If you have summoned it and you help kill it then it locks you out from doing the event again. If you are after EoW and other players show up do not attack.
Do it in WM, much more likely to have either no one or only 1-2 other players that you might be able to convince to let you tame, since it spawns about 10 secs after it’s been tamed
I was in WM. I wanted to tame it, but everyone would show, and kill it. I turned it on then when I collected the flowers I could not throw them in. So I had to find out the hard way that you can only summon EoW once a day.
Yea it sucks that you can only summon him once a day, but give it a week or two and people won’t be farming the rares so much, you’ll get it eventually 
So is Envoy once a day or once a week? I get conflicting information.
For the last couple days the quest has been active on my map now and then, the flowers clickable, but I can’t toss the flowers into the pool.