My Little Monster-Sitter is the 2nd book in the Papercutz series of graphic novels. The introduction describes Mavis as being 114¾ indicating it takes place before she turns 115 in Fangceañera, adjacent to the events in the preceding episodes of Hotel Transylvania: The Series.
It also references Lydia Dracula as being summoned from "12th century Transylvania". Since Lydia is over 1200 years old, this is not when she was born, but probably refers to when she decided to start a long stasis-sleep, which she is shown waking from in the series opening music.