I started collecting a couple of weeks after the Snowy Owl went into hibernation. It was one of only two pets I needed for months to complete the Zookeeper. The good thing about needing it was that it kept me from getting too frustrated about that misbegotten Minfernal. Once I finally got that sorry pile of rocks it was a little annoying to have to wait for the Snowy Owl, but at least the end was in sight and I knew when it was coming.
However; if you think nine months is too long to get an achievement, don't, repeat don't bother with the three year Children's Week pet achievement.