
I'm with Marianne on this one. Lots of large breed owners will say that the first two weeks are the most important. But we are talking about very tiny pups here.
Remember that they don't have a thermostat for the first 21 days, and that is going to be more dangerous for body temperature to drop too low in these little widgets. I recently saw an advert for viewings of this breed at 16 days!

Hells bells, you don't even know if they're going to live at this stage!
So I have my beady eyes on them throughout the whole of the first 3 weeks. And, even then, underbed heating doesn't go. I just won't risk it. I am most certainly not paranoid, and I am pretty laid back with litters, but still consider that I owe my girls the utmost vigilance, after all, it's my fault that they're in this situation! Fortunately, my calmness rubs off, which is a bonus for them. Glad to see that another poster doesn't mess with pups all the time (apart from weighing.) I cringe at the thought of them being picked up all the time, and moved away from the heat source that they need.
My last litter had 2 pups that still only weighed 500gm at 10 weeks, and, although mine get well socialised with Collies by this time, I am still very much aware that my largest Beardie sitting on them isn't a good idea! ;-) :-)
I think it's very much just a common sense approach needed due to sheer size. I am amazed when I see these breeds advertised at 6-8 weeks old. Have to say that, although the breed club advises 12 weeks, my last litter needed a little longer. If people push to have a puppy younger than I am willing to let go - I tell them to go elsewhere! It's so easy to do, as litters are so small, and I like to take my own sweet time on choosing mine! :-) :-)