Use the adjective round-the-clock to mean always, at any time of day. A security company that uses round-the-clock surveillance is keeping an eye on things 24 hours a day.
Round-the-clock flights to New York leave all day and all night long, and a diner that offers round-the-clock breakfast will serve you pancakes whether it's six in the morning or midnight. If a patient needs round-the-clock care in the hospital, they'll have nurses checking on them nonstop, day and night. Round-the-clock dates from the 1940s and was first used to describe air raids during World War II.