I take all pups out and into a carrier bin , and then I have a 2nd empty carrier bin to which I place the handled pup into after the handling. This assures I am handling every pup and not just the same friendly one over and over(comes in handy when you have a litter of 10 same color pups)
Handling time starts at no more then 5 minutes twice a day, on day 18 then progresses to about 10 minutes as they age and are weaned from Mom. By the time they head to a new home they are completely relaxed at being picked up from above, and related a human hand with good things.
Just and observation I have seen in Yellow based pups, They tend to need more handling, more often and the first handling session almost always results in being peed on LOL I have no idea why this is but any other color without the Yellow gene they never pee on me at all and accept handling like it was done all their lives.
Oh I also don't use food as I have found it often lead to nippers when they didn't get something to eat before handling them. Many started connecting the food with the hand and tasted the fingers looking for food. Also I think about young owners and what might occur if their hand smells of a tasty treat when none was there. However mine learn that if you allow the human to pick you up an hold you that after they are done holding you a bowl of Noms awaits you back in the bin