Employees have gained increased flexibility in organizing their work in time and space, that is boundaryless work. Managing the boundaries between work and personal life would seem to be crucial if one is to psychologically detach from work during leisure in order to unwind and get sufficient sleep. Drawing from a sample of Swedish professional workers (N = 3,846), a theoretical model was proposed testing the inter-relationships between boundaryless work in time and space, weekly work hours, psychological detachment, sleeping problems and sleep duration using a structural equation modelling (SEM) analysis. Findings showed that working boundlessly in time, that is spread out during the working day and week, was directly associated with both long weekly work hours and lack of psychological detachment. In contrast, working boundlessly in space, that is at several different places, was inversely associated with weekly work hours and had no association with psychological detachment. Psychological detachment, in turn, was directly associated with sleeping problems and inversely associated with sleep duration. Sleeping problems were inversely associated with sleep duration. Employees with long weekly work hours had a low degree of sleeping problems. There was also no association between long weekly work hours and sleep duration. These findings contradict earlier research, however, we interpret these findings as that if one works a great deal but is able to mentally detach from work-related feelings and thoughts during free time, then sleep will not be hampered because perseverative cognitions associated with prolonged biological activation will have been interrupted. As such, psychological detachment can be regarded as the mechanism that mediates the relationships between working 'anytime' and long weekly work hours, and sleep. It was concluded working boundlessly in time increases the likelihood for long weekly work hours and lack of psychological detachment. Hence, employees working 'anytime – all the time' run the risk of 'always being on' resulting in disturbed sleep.