my grand baby is 16 mo old what is the best dau to wean off the bottls

I was wondering if there is a best day chart to begin to toilet train a child? I remember calling my Grandmother, who hung her almanac by the telephone, to ask her when to potty train my kiddos. She would look up something and tell us when. It worked! I am not sure if she based it on something else that correlated with it or not, for instance "wean animals or children". Would you happen to know? Thank you for your help! ~Gail McDermott