Yes, It was happened for my nurses in my country, Cambodia, and still be existing until now in some hospital both government & private sectors. because of nurse shortage, we applied the model of "Round-the-clock". Nurse must stay in hospital for 25hs (1h for changing shift report) on the day of their duty every 4 days. However, you are right, they can take a short break to sleep if their patients are in stable condition. After 24hs, they have taken 1 day off and continue their working day as routinely. Their working day is 4h per day, and for duty day is 24hs. The duty day is every 4 days. But currently, there are some changing in some hospitals. They develop 2 shifts/day, 8hs for day shifht & 16 hs for night shift, because based on the safety in transportation, they can not work as 12h for day shift, and 12hs for night sift. I think it might surprising you, but it is real situation of my nurses here.