Are the newbies young pullets, I wonder, Tweak? This may be a factor, if they're not yet laying, as they will give off immaturity signals and be more submissive and less confident and able to stand up for themselves. If they are less than 20 weeks and still growing, they will be helped if you can keep them apart until they are more mature. Don't worry if you haven't got a proper coop, you can improvise a waterproof box with some comfortable bedding for them to sleep in, and perches are not essential at that age and for a short time. I think people usually keep them apart for quarantine reasons as much as to let young stock grow on a bit, and also perhaps to give them a course of flubenvet wormer before they go into the flock, as this takes a week anyway and gets them off to a good start in a new environment healthwise. So this quarantine factor probably accounts for the variation in times you've been quoted, as some people just trust to luck and don't do this, whilst others give up to a month in some cases where the place the birds came from might not have been ideal (eg a poultry auction.)
I've found it helps to get them used to seeing each other through the wire, as you have done, and also putting vinegar on all the hens' feathers before moving the newbies in to the coop after they've all gone to sleep, as Lordcluck suggests. then I expect you've tried putting out several feeders and drinkers, also scattering food on the ground helps as the old hens can't get everywhere at once and the young ones get to feed better. I know this isn't normally good practice but it does help integration for a day or two. I also keep a careful eye on them, and give the youngsters 'time out' for an hour or so during the first day or two, behind a netting barrier, to rest, feed and recover, before putting them back when I'm about to feed the older hens some scattered treats eg a handful or two of mixed corn. Providing perches which are low enough for the youngsters to fly up to, but too high for the old hens to bother about, also helps as a refuge, as does sufficient space in the run for them to get away, and places for them to hide behind, eg a temporary screen across a part of the area or a box or two. It's a distressing time, isn't it, but all new girls get a run around and the thing to do is keep watch, let them get on with it unless someone is actually being badly bullied (ie held down and head pecked repeatedly) or actually injured, and if it's bad, make sure they've had a few sessions of time apart to feed and drink and rest now and then in the first day or so. Space is very important - how big is your run I wonder? They do need a minimum of 2 sq.metres each, more is better to reduce aggression problems.
