[LunarBerry]

I'd say it depends not only on the age of the yorkie but also what the yorkie themselves are used to or capable of. In the beginning, in my personal opinion, is the most crucial in bonding and also creating a sense of security for them. If you can't give the time or at least not mind that someone else could cover for you (which might cause them to bond more with that person) then it's best not to do it. Such situations would have to be gradual to allow them to get used to solitude (unless they naturally or already prefer solitude)
These furbabies, rarely deal with being alone very well for so long the younger they are, at least in my experience. It's not as bad if there's other dogs/playmates with them. But from experience I had my yorkie baby by herself completely for the first time (at the age of 5 months) when taking the other older dogs for nail trimming for 30min to almost an hour and she was literally crying when we came back. Not all yorkies are like this, of course, but the younger they are, the most likely they'll need the have someone there with them often., if not at all times.