本文追溯社會資本的原初定義、釐清其主要成份，並以「家人重疊網絡」為範疇，探討社會互動中的「時間投資」機制。文中依據兩筆人際接觸日誌（接觸數分別為2,233和1,555），分析社會行動的基本單位（接觸）如何隨著投入時間而變化，這些變化又如何反映出重疊網絡的特色。細究兩位報導人對每次接觸的主觀感受和評價，發現不論親疏遠近、只要接觸時間愈久，報導人對於該次接觸的情感涉入就愈深，也愈加肯定接觸的意義。時間投入的效應，在不重疊網絡和中度重疊網絡中相當明顯，在高度重疊網絡中卻大為減弱。重疊網絡中業已鑲嵌可動用之社會資本，不必在日常接觸中刻意投入時間資源來獲取報酬。「投入時間」定義清楚、標準一致、測量容易，其形成背景具有明顯區辨能力，也是主觀感受和評價的重要考量因素，成為衡量社會資本運作的一項重要指標。將此指標應用在不同重疊程度網絡中的人際接觸，更能彰顯社會網絡觀點的研究與測量特色，進而對於社會資本如何實際運作，提供有力例證。

Conceptualizing the study of social capital relies on untangling the various mechanisms that help accumulate and capitalize social resources. Based on the social network perspective, this paper first clarifies the core concepts associated with social capital and differentiates its major components. It then examines how actors gain from investing different amounts of time in social interactions within three kinds of networks: highly overlapping networks, somewhat overlapping networks, and those that do not overlap. The data were drawn from two contact diaries (with 2,233 and 1,555 contacts, respectively), which recorded the actual amount of time each contact lasted, the immediate returns from each contact, the sociodemographics of both the ego and the alter, and the relationship between the two actors. The findings indicate that, under similar sociodemographic, relational, and contact circumstances, the ego tends to experience more expressive and substantial gains when a contact lasts longer. Such a duration effect disappears, however, when either actor knows the other's very well. This nuance suggests that overlapping networks are usually richer in social capital; thus actors feel a less urgent need to invest time when they wish to obtain immediate returns, as other studies also have shown. As an objective, standardized, and universal unit, time investment is easy to measure. More importantly, not only does time investment vary significantly on different individual and relational factors; it also clearly differentiates how actors perceive and evaluate each specific contact. Time investment is a key mechanism in social capital, particularly amid overlapping networks, and this measure helps showcase how social capital functions according to the network approach.