Chat communication is often fast-paced, creating the expectation of quick replies. While the timing of exchanges is known to foster closeness and enjoyment, it remains largely unexplored whether chat partners with strong ties reciprocate each other's response times. Using 3.4 million messages from 889 chats across 97 donations of anonymous WhatsApp and Instagram chats, we analyzed response times, their balance between chat partners, and its stability over time. To our knowledge, this is the first study to examine response speed as an expression of reciprocity, bridging a key aspect of online communication with a fundamental principle of social interactions. We found that around 70% of WhatsApp and 44% of Instagram messages were answered within five minutes, confirming the fast pace of instant messaging. Overall, the response speed between chat partners was similar. The response speed similarity was evident both in the overall response-time distributions of chat partners assessed with Jensen-Shannon distance and in the steep regression slopes (0.786 for WhatsApp and 0.796 for Instagram) linking one person's probability of responding within five minutes to the partner's corresponding probability. Importantly, the dispersion of response time similarity over months showed that this balance persists over time. Our results position response time balance as a marker of reciprocity in computer-mediated communication, offering a new way to quantitatively study this fundamental principle of social interaction. We suggest using response speed balance as a complementary metric in the analysis of relationship dynamics, such as the strengthening or weakening of social ties.

翻译：聊天通信通常节奏较快，从而催生了快速回复的期望。尽管回复时机的把握已知能增进亲密感和愉悦感，但具有紧密关系的聊天伙伴是否会相互呼应对方的响应时间，这一问题在很大程度上仍未被探索。利用来自97次匿名提供的 WhatsApp 和 Instagram 聊天记录的889个聊天会话中的340万条消息，我们分析了响应时间、聊天伙伴之间响应时间的平衡性，以及这种平衡随时间变化的稳定性。据我们所知，这是第一项将响应速度视为互惠表达的研究，它将在线交流的一个关键方面与社会互动的一个基本原理联系起来。我们发现，约70%的 WhatsApp 消息和44%的 Instagram 消息在五分钟内得到回复，证实了即时消息的快速节奏。总体而言，聊天伙伴之间的响应速度相似。这种响应速度的相似性，既体现在通过 Jensen-Shannon 距离评估的聊天伙伴总体响应时间分布上，也体现在连接一方在五分钟内回复概率与另一方相应概率的陡峭回归斜率上（WhatsApp 为0.786，Instagram 为0.796）。重要的是，响应时间相似性在数月间的离散程度表明，这种平衡随时间持续存在。我们的结果将响应时间平衡定位为计算机中介通信中互惠的一个标志，为定量研究这一社会互动基本原理提供了一种新途径。我们建议将响应速度平衡作为分析关系动态（例如社会关系纽带增强或减弱）的补充指标。