I used to check throughout the night when we kept Jacobs - one of the reasons we stopped keeping them. For the Hebs, Soays, Shetlands we checked last and first thing.....until last spring when our very first ewe to lamb was a first-timer in the night, in a big storm, and we lost one of the lambs to hypothermia. For the rest of that lambing I checked every two hours every single night but not one lambed during the night, and every time I went out into the field in my jimjams (with a coat over) and a giant torch plus dog who won't be left behind, it disturbed the whole flock. So this coming spring I will be back to checking at midnight and 5, and will only go back out if someone is looking likely.