How long plush restock takes?

That depends. Both Bluestar and Hollyleaf are already availabe again/have been restocked once more due to just how fast the first batch of them was sold out only like two days after they had launched. You can pre-order them now and they will get shipped mid January next year (so early 2023). Same with the new Yellowfang plush although that one is going to ship at the end of January and also is not a restock but a first launch instead.

Other restocks of older plushie launches also depend on popular demand of each character. For example, Firestar, Jayfeather, Brightheart and Scourge were restocked at least twice this past year (I finally got Firestar and Brightheart due to that) and might get restocked again if the demand is high enough next year as well. But other cats such as Graystripe, Squirrelflight, Ravenpaw, Leafpool, Cinderpelt and Ivypool have not been restocked so far for what ever reason (considering how popular some of them are and how people have been requesting restocks for them on other sites such as instagram).

I did this the same way for Firestar but the actual email from the website alerting me to him having been restocked actually got sent a few days after he was already sold out again (thankfully I got alerted to him being restocked alongside other characters via a tumblr post before that where a user had just announced they had finally bought Scourge who had been restocked as well). So yeah, there's that to consider about these emails since they might not get sent in time. Just as a heads up.

Also, just saw by checking one of my threads about merch from this year, that Leafpool was available this past August. But only on the International Store though:

wcrpforums.com/thread/89377/merch-discussion-heads-plushies-restocked

oop. Hey! Scourge plush toy has been gone for a long time((Maybe you know he will appear back in the future?