I think a lot depends on how many ewes you have, how quickly you expect them to lamb and how willing you are to risk losses, mismothering and aggravating problems that don't get picked up quick enough.
As already said if you are lambing outside, you need to look round last thing and just before dawn (before the crows get out of bed) although if your ewes are in a field nearby and you have a very powerful torch, you ight just want to shine the light round in the middle of the night so you can check without having to disturb the sheep.
Indoors - well I can only tell you what we do. We had 180 ewes to lamb and all bar 14 of those to lamb in a fortnight, sso quite intensive. Once it gets busy either myself or my OH are on duty 24 hours a day, although we may not be in the shed, we will be about, or grabbing a quick 20 minute kip on the straw stack. Both of us manage about 4 hrs sleep a night. Now it has eased off, and we only have a dozen or so left, they are being checked every 1.5 hrs, with us taking it in turns so we are getting 2 three hours stretches of sleep each, per night, or thereabouts.
Our ewes rarely need assistance, but we feel that to loose a lamb just because we weren't there or were in bed is a bit slack really. Most of the year the sheep pretty much look after themselves, but a lambing time, we owe it to them to make sure they get the best of care. Given that we have only lost three lambs out of well over 200 hundred born suggests it works (and those were all premature low birth weight lambs).
Yes it is KNACKERING, but soon it will be done.