When should I add cherry extract?

I have a dark cherry stout kit from NB that I started yesterday and is fermenting away. The recipe says to add the cherry extract to the bottling bucket. I am wondering if this is a good idea or if I should add it to the primary after three weeks or so that the extract can sit in there and bulk age for another two weeks or so.
The main problem that I see with this is that I might not be able to get it mixed in well without disturbing the yeast cake, which means that I won't be able to taste it and judge how much I want to add. I guess I could bulk age in a secondary for weeks 5-7 or 8.
Has anyone else made this recipe? If so, how much cherry extract did you use? Any opinions in general?

Extract flavoring should be added when packaging. Put it in the bottling bucket like the instructions say.

Do you have an estimate on how long it takes for the extract to blend in well. I know that it's going to vary, but I'm guessing that the late introduction of the extract will mean that it takes that much longer for the flavor is balanced out. So, ballpark?

I just made this kit, added it at bottling with the priming sugar. Poured the extract in the bottom and racked onto it, pretty well mixed I believe due to the whirlpool effect. Just went for it and added all 4 oz, 2 weeks after bottling its still a little rough, kind of medicinal tasting (cough syrup). Would be glad to answer any other questions.

Amusingly enough, after typing that I cracked another bottle... just to make sure. 3 days after my initial tasting it has improved quite a bit. That might be because I tried it after a handful of other refreshing adult beverages (I know, I know sub-par tasting environment), but this one is quite tasty.

Thanks dlloyd. I think I'm going to be conservative with the extract since this is my first time making a "flavored" beer. I think I'll add about 1oz, mix and then taste.
Did you taste it from the bottling bucket before you bottled to see how strong the cherry flavor was? I'm wondering what to expect in the bottling bucket so I can try to gauge how strong the cherry flavor will be after letting it mellow out. Ideally I want a just a bit more than a hint of cherry after aging to maturity.

To be honest, it was the second 5 gal batch I bottled that night, was a little sloppy, didn't taste it before bottling. I just dumped all 4oz in. Like I sad before, its getting much better, even in this short amount of time. The taste was quite medicinal at first, now its a bit more mellow, still with an odd aftertaste. Hopefully it will further improve.

I'm getting ready to brew a batch of cherry ale and will be using a liquid cherry extract as well. Do you recommend pasteurizing the extract before use? Also, what about adding the extract at flame-out?