Horgan tells Dan it must have been 15-16 years since they've seen each other. Later in the same conversation he says he's been a lawman for 20 years, so he was a rookie himself when he trained Dan. In The Long Gun (1962), which took place about 3 years later, Dan tells a visiting lawman he's been a lawman for 20 years, which aligns with the stated time frame here, but would also mean Dan spent very little time with Horgan.