I have not had much experience, however, i have sucessfully trained all of mine from 8 weeks. That is the ones that live with me & the litter I had were trained before leaving at 8 weeks. The odd accident has happened when I haven't been vigilant. The dogs that live with me I simply took to bed from 8 weeks, as soon as they stirred I very quickly carried them outside onto the grass & told them to go "tooty". I realise this may not work for everyone, but I found it worked very well. I knew if I didn't get up straight away I would end up sleeping in puppy piddle. I think because it was at night I was consistant, whereas during the day you get distracted by all the usual day to day chores etc. It doesn't take long - maybe a few weeks. I didn't feel like doing it with the babies I kept from my 1st litter,I was exhausted from running around after my three year old daughter all day. I did it anyway & it worked great. The other thing you could try would be a puppy pen with a very thick layer of newspaper. When puppy has done business take the paper outside, & then everytime you take it out for toilet break take to the newspaper.
I think leaving puppies running loose in the house at that age is a bit of a risk for toilet accidents.
Goodluck & heres to less puddles.