lights–out 
/ˈlaɪtsˈaʊt/ noun
/ˈlaɪtsˈaʊt/ noun [noncount] : a time when people (such as soldiers, prisoners, or students) are required to turn out the lights and go to bed
▪ Lights-out is at 10 p.m. ▪ They have to be back before lights-out.
▪ Lights-out is at 10 p.m. ▪ They have to be back before lights-out.
