It really varies by section.
Some sections have a single "advancing to Nationals" Men's/Women's season, typically in the Spring, some in the Winter, and some even as an early start league in the Fall of the previous year. But there are some sections that have multiple seasons that can advance and will have them in Spring, Summer, Fall, and Winter.
The also depending on the section, there are "other" leagues such as Tri-Level, Combo, Singles, or just other local leagues that go on at various times of the year, often filling in the spot in the calendar when the "advancing" leagues are not taking place. And of course there is Mixed as well which can take place at varying times of the year depending on section again.
NTRP FAQ