At which hour is recommended to go to sleep?

Sleep 10pm to 6am. Sleep schedules vary depending on the work schedules and school schedules of people in the family. In general, one aims for 8 hours of sleep (7 may be ok, but less than 7 can make one tired during the day). That can mean 9pm to 5am, or 10pm to 6am. Going to bed at the same time and waking up at the same time, every day of the week, is good for one's natural 24-hour sleep/wake cycle.
no recommendation. No such recommendation. Also length of sleep is individualized and can't be prescribed as a blanket order for every body.