เวลาพลบค่ำอันเงียบสงบ

Investigate the Radio in the Parlor Car, and listen to it fully, taking ~5mins OR click investigate twice to immediately obtain the achievement.

In the context of television and radio, "prime time" refers to the period when the largest audience is available. This is typically the evening hours when most people are done with work and are likely to be watching TV or listening to the radio.