The rescuers have been learning from experience and were two hours faster in bringing the second batch of survivors out on Monday.
Five people are still trapped inside the cave.
Rescued schoolboys are moved from a military helicopter to an awaiting ambulance at a military airport in Chiang Rai, Thailand, July 9, 2018.
Four more boys were rescued overnight after the first four emerged yesterday. He was taken by helicopter and then ambulance to the hospital in Chiang Rai were the first four boys, who were rescued on Sunday, are now being held in quarantine as they undergo tests. Each of the rescued boys has been guided through the dark winding cave by a pair of divers. Two of them possibly have a lung infection but all eight are generally "healthy and smiling", he said.
All preparations, including replacing the oxygen cylinders positioned along the route out in the cave, take at least 20 hours, he said.
Four fellow teammates and their coach, Ekaphol Chantawong, remain inside, with hopes that they will be rescued on Tuesday. He said recent rains had not affected water levels in the cave and conditions were expected to be "as good as they were on Sunday", reported The Guardian.
Four boys and their 25-year-old soccer coach remain deep in the cave, an ordeal that has lasted more than two weeks after they were trapped inside by floods.
The group was found nine days later in a cramped chamber 2.5 miles inside the cave system by two British volunteer rescue divers.
The leaders overseeing the desperate and unsafe rescue of 12 young soccer players and their coach from a flooded cave labyrinth in northern Thailand were only half joking when they quipped that success was in the hands of the rain god Phra Pirun.
Even tech billionaire Elon Musk has been lending a helping hand. On Sunday, he shared photos and video on Twitter showing a "tiny, kid-size submarine" that could potentially help with the rescue effort.
The boys, some of whom don't know how to swim, have also been taught diving techniques to prepare them for their hard journey home.
At a news conference, Jedsada Chokdumrongsuk, permanent secretary at the Public Health Ministry, said the first four boys rescued, aged 12 to 16, are now able to eat normal food, though they can't yet take the spicy food favoured by many Thais.
The names of the rescued boys have not been released out of respect for the families whose sons were still inside, and they have not been reunited with their own families, he added.
Interior Minister Anupong Paochinda said the boys were generally "strong and safe", and under close medical supervision.
People across Thailand cheered the rescue operation, including at the Mae Sai Prasitsart school where six of the trapped boys are students.