Since the 1970s, part-time employment has grown in the German and French labour markets. The relation between public intermediation and part-time employment is the subject of this thesis. Our comparative analysis is based on ethnographic immersion in four agencies, a quantitative analysis of 2000 job offers stored in the agencies files and a socio-historical inquiry concerning the unemployment benefit systems. With these data, we expose the temporal transactions experienced by the unemployed during their institutional treatment. Within the agencies, the working hours sought by the unemployed represent a tool with three functions: managing the registered users, matching employers and jobseekers, and arbitrating the relation between capital and labour. These hours are mobilized, manipulated and negotiated during the compulsory interviews between caseworkers and unemployed. Thus, many research profiles are modified, in the sens of lowering the desired amount of employment hours. This rationing of hours is organized around three modes of regulation, always perceptible but inequally significant in the various agencies: benefits-oriented regulation, professional regulation and computerized regulation. The working hours the unemployed look for appear as an object of public action. Based on our empirical results, we show how the configuration of bureaucratic encounters establish a close relation between the social resources mobilized during the interaction and the position on the labour market. In addition, this thesis present the employment agencies as an autonomous level of employment regulation.