Background: Prevalence of sedentary behaviour is high in many countries, but little is known about temporal trends in sitting time. Objective: To examine temporal changes in sleep and domain-specific sedentary behaviour and moderate to vigorous leisure time physical activity (MVPA). Methods: Two cross-sectional population-based surveys of 25–79-year-old inhabitants were conducted in The Capital Region of Denmark in 2007 (N = 69.800, response rate 52.3%) and 2010 (N = 77.517, response rate 54.8%). Information on sedentary behaviour and physical activity was obtained from self-report questionnaire and sociodemographic information from central registers. Data were weighted for survey design and for non-response and were analysed by multiple regression analyses. Results: In 2007, the entire survey population reported a mean daily sleeping duration of 7.4 hours, leisure time sitting of 3.4 hours per day, occupational sitting of 4.4 hours per day, MVPA of 0.87 hours per day and a total 24-hour energy expenditure of 40.12 METs per day. In 2010, duration of sleep was unaltered (p = 0.1), sedentary leisure time and sedentary work time had increased by 12.6 minutes (p < 0.0001) and 13.2 minutes (p < 0.0001) per day, respectively. Time spent on MVPA had increased by 2.9 minutes per day (p < 0.0001). The 24-hour energy expenditure had decreased by 0.41 METs (p < 0.0001). Conclusions: Adult Danish men and women spend an increased amount of time sitting down at work and during leisure time, but also on leisure time MVPA. As duration of sleep is unaltered findings suggest that low intensity physical activity may be displaced in everyday life.