Thousands of olive ridley sea turtles came to La Escobilla beach in Oaxaca, Mexico. Sanctuary officials said the turtles arrived within 48 hours to lay their eggs.
within 48 hours= 48時間以内(ある時間枠を超えないことを示す表現)
This natural event is called "la arribada," which means "the arrival." During this time, hundreds of thousands of turtles swim ashore in southern Mexico.
swim ashore= 海から陸地(海岸)へ泳いで上がる
This is the sixth wave of turtles to arrive during this nesting season. The season started in March.