"Back in the day,” said Lim Hyung-kyu, a retired Samsung Electronics executive now in his 70s, "my weeks were Monday, Tuesday, Wednesday, Thursday, Friday, Friday, Friday.”

Lim joined Samsung, South Korea’s largest company, in 1976 and rose through the ranks to chief technology officer.

For much of his 30-plus years at Samsung, working on the weekends was normal — and legal under the nation’s labor laws.