Attachment is lifelong. It's not just “one year, 365 days and the job's done”. Attachment is something that needs to be constant. The first year, of course, is very critical, as I have said numerous times, especially when we are looking at children who may have experienced trauma. It's important to have that time with their family to work through that, to help them feel comfortable, safe and secure. There isn't just a number: “Oh, 365 days: Check. I'm attached. I'm good.” It's something that continually goes on and on.
In parenting specifically, that's why we definitely want to have an attachment with our children once they get into those teenage years when kids sometimes have more difficult experiences in schools and such. It's good to have that attachment and bond secured so that parents can be there to help guide their children, have conversations with them and grow their relationship with them throughout life.