Piltzintecuhtli takes the third turn in the nine night rotation, governing every ninth date beginning from the third day of the 260 day tonalpohualli and recurring on a different day sign and trecena each time the short cycle completes, since nine and 260 share no common factor and only realign after 2340 days. His position immediately follows Itztli, the obsidian blade, and precedes Centeotl, the maize god read in some accounts as his son, so the sequence Xiuhtecuhtli, Itztli, Piltzintecuhtli, Centeotl can be read as fire, the blade, the dawn and the harvest in unbroken order, a progression later interpreters have found suggestive though Sahagun's own text presents the nine simply as a fixed list rather than a narrative.
A date falling under Piltzintecuhtli's night was read, per the general logic Sahagun's informants describe for the tonalpouhque's craft, as tempering whatever the day sign and trecena already indicated with the character of youth and new beginning, gentler than the days governed by the death lord or the blade. The calendar priests worked from painted tonalamatl books that set out the full nine lord sequence beside the twenty day signs so that the correct night lord for any date could be read directly rather than calculated, and it is this practical, tabulated use, rather than any independent festival, that is the best attested feature of Piltzintecuhtli's place in Mexica religious life.
Sources Cycles of Time and Meaning in the Mexican Books of FateElizabeth Hill Boone with Florentine Codex: General History of the Things of New SpainBernardino de Sahagun; translated by Arthur J. O. Anderson and Charles E. Dibble