Well, without more context, it's difficult to say precisely. '5th quarter' might be a metaphorical term. It could be a true story about a group of people who found themselves in an unexpected or 'extra' situation, similar to how a fifth quarter in a game would be something out of the ordinary. Maybe it's about a post - game event that had a big impact on the people involved.
I'm not sure specifically what the '5th quarter true story' is about as there could be many stories with this name. It might be related to an extra period in a game (like in sports, though usually there are only four quarters), or it could be a unique story about a particular community or event.
Chapter 731, "Ye Chu Died", is the clearest early answer because it turns Aunt Xu's situation into a concrete plot event. The chapter turns that into something concrete by moving from Dean, can I really not do it? to She'd been acting off these days..
Chapter 639, "Young Master Gu, Does Your Family Need a Dog?", is the clearest early answer because it turns Shang Shuyue's situation into a concrete plot event. The chapter turns that into something concrete by moving from Half an hour later, Jiang Li pushed open the door and walked out.
Chapter 908, "Wrapping Up Successfully!", is the clearest early answer because it turns Jiang Bufan's situation into a concrete plot event. The chapter gives readers a real answer by opening on Jiang Mingchuan, after a busy day, also returned home.
Chapter 740, "Someone Who Can Live Through the Days", is the clearest early answer because it turns Fang Kai's situation into a concrete plot event.
Chapter 826, "Deadlock", is the clearest early answer because the violence around Yu Li becomes final instead of hypothetical. The chapter turns that into something concrete by moving from The Li Family Master had spoken, so Father Yu quickly followed suit...
Chapter 705, "Is She Her Own Destined Noble Person?!", is the clearest early answer because it turns Chen's situation into a concrete plot event. It opens with He Wen was made to laugh by Bai Lu. and closes on Outside the building, Zhao Lang gazed thoughtfully at the car parked....
Chapter 685, "Defense Value Skyrockets!", is the clearest early answer because it turns Jiang Yan's situation into a concrete plot event. It opens with The scene went live on Weibo right then. and closes on How could he not be furious?.
Chapter 827, "Mystical Event Investigation Bureau", is the clearest early answer because it turns Qixing Tower's situation into a concrete plot event. The chapter gives readers a real answer by opening on Jiang Li's words indeed make sense.
If you want the clearest chapter reference, go to Chapter 17. Early on, Jiang Li glanced at Jiang Shixu, who was tense and anxious behind her, and...; later, the chapter leans on Okay, let's go eat." After speaking, she strode forward..
Chapter 713, "Uncle Will Owe You for Life", is the clearest early answer because it turns Zhao Lang's situation into a concrete plot event. It opens with Jiang Li raised her head and was startled by Zhao Lang's smiling eyes.