You could spend as little as two days and as much as two weeks or more exploring the Nayarit Coast , depending on your interests. If you have only two days, best go by tour or car, stopping at Sayulita  or San Francisco  for lunch and a stroll and sun on the beach, then continue north for an overnight at Casa Pacífico or Mar de Jade in Chacala .
The next day, continue along the Bay of Matanchén, to San Blas , for the unmissable jungle boat tour  and lunch (four hours) at La Tovara spring. Return south through Tepic  and, time permitting, enjoy a (two-hour) detour to gorgeous volcanic Laguna Santa María  en route back to Puerto Vallarta .
With a few more days, you could add an overnight or two at Sayulita and/or San Francisco. Be sure to include a visit to the nearby Alta Vista Archaeological Site .
Continuing north to San Blas, between August and December, stop by (two hours for a look, or overnight) at Playa las Tortugas  vacation home resort and the adjacent turtle conservation center.
Spend a few nights farther north at San Blas, which you can use as an excursion hub for wildlife-watching, beach swimming, sunning, and strolling, and adventures farther afield to the Huichol Cultural Center  in Santiago Ixcuintla  and the historic and picturesque island-town of Mexcaltitán  for perhaps an overnight.
Return south, via Tepic, stopping for lunch and shopping for Huichol handicrafts. Continue to Laguna Santa María for at least an overnight. Spend your last day swimming and boating on the lake and strolling its lush, forested shoreline.