Well, the rice starts cooking in cold water ~ that's already some 10 mins before it gets boiling hot and turn it down to "慢火20零分鐘" - so the whole cooking time is easily 30-40 mins ga, the rice is soft/棉. For 6-month-old, I think I used to 慢火30-40零分鐘 (definitely not more than 1 hour!) to get it more 棉.
Sometimes I find that even I have boiled the rice for 個幾鐘 the rice is still not 棉 because I can't get the right heat and the right amount of water. The rice do not become 棉 by using high heat for long hours ~ it is just very difficult to explain. With more trial and error, you will get the hang of it la!