This paper studies how apps compete for user time and welfare implications of mergers of free apps. I develop a discrete-continuous model of time allocation with a binding time constraint. I estimate the model on three pairs of apps (substitutes, complements, and a pair with an ambiguous relationship) with a panel of app usage in China. I use updates as instruments to disentangle complementarity from correlated preferences. I recover reasonable competition patterns. Merger simulations suggest that users will face higher prices (more ads) after a merger of WeChat and Kwai though they did not offer similar functions.