Columbus's arrival in the Caribbean, by sheer luck, hastened the conquest of Mexico significantly. Without his stupid ideas about the circumference of the Earth, it's quite likely that European colonization in the early sixteenth century would have happened only in Brazil and the northeast.
So, assuming Columbus dies (maybe he's killed by the Taino) and never returns, when do Europeans conquer Mexico? That is, by which decade in the sixteenth or seventeenth centuries will Europeans either
1) have conquered the Aztecs, or (if the Aztecs collapse before Europeans arrive),
2) control the majority of Mesoamerica?