Day-1

Depending on your geographic location, culture and political views, starting potty training at the tender age of 2 ½ years is either way too early or far too late.
For us it felt about the right time, perhaps a little past its due date but still within the realms of timely. My main concern was not with giving my children a sense of control and mastery of their sphinctoral muscles, no for me the urgency was purely financially driven. Those doughy rectangular blocks of absorbent goodness are really expensive.
I recently went to a Turtle sanctuary/hospital with the kids, called Gumbo Limbo. There you can find tanks of various fishes, turtle hatcheries (is that the correct term) and an interesting ongoing display of man-made elements and how long it take for them to decay in the environment. You walk past a wall with these elements of detritus nailed to it
When you realize how bad they are from the environment the way forward is clear.