This article examines the paradoxical impact of emerging communication technologies on social cohesion by investigating the struggle to standardize Ramadan observance among Chinese Hui Muslim communities in the early twentieth century. Reform-minded Hui intellectuals hoped that modern media, such as print periodicals and the telegraph, would disseminate moon-sighting news and unify the diverse temporal practices of Hui Muslims across China, thereby forging a modern, unified Hui identity. However, this article argues that these technologies did not lead to seamless temporal homogenization. Instead, they amplified local divisions and precipitated a crisis of authority by forcing Hui communities to confront a new and divisive question: who and what to trust in a new information landscape? Drawing on case studies of disputes in Guangzhou, Xi’an, Beijing, and Chengdu between 1931 and 1934, the article demonstrates that Hui Muslims’ trust was not monolithic but fragmented along lines of faith in the communication technology, the messenger, and the information itself, which in turn prevented the implementation of a standard Ramadan temporality. By centring the analysis on the social dynamics of trust, this article contributes to the history of technology and media studies, revealing that the adoption of technology is fundamentally a process of building, challenging, and negotiating authority through the fragile and fragmented medium of trust.