When the movie has been deemed a hit. They will probably see how merchandise is selling first before making decisions on character appearance.
The only character whose recent film was successful enough was Maribel from Encanto, and it took about 5 months.
The last Pixar new characters to meet were Joy and Sadness in Hong Kong, a few months after the movie came out. It took about 3 years after the release of the movie before Joy started meeting in US parks (I think).