The article strives to demonstrate the centrality of the category of social time (a) in people's daily lives, (b) as a methodological tool in the study of social process, and (c) as a means towards the planned development and management of advanced societies. Social time has two aspects: rhythm of life and available total time. The article shows that in advanced societies total time and its rational allocation are central in the development of society and individual personality. The nature of social time in less developed societies is also reviewed as well as the historical development of time awareness and the problems of the research on time budget. The article is based on the conceptions about the nature of the economy of time that emerged from reading Marx's Grundrisse.