Let the plants grow until the mother leaf dies. At that point, you will know they have root systems capable of supporting them. Plant them at the same depth they were in the 'mother pot', don't cut the roots off. That defeats the purpose of spending the time and effort to growing roots.
If you have already unpotted them and taken them apart, I'm not sure what the chances of survival will be. I usually wait until the planlets are blooming to separate them. Then I know which ones are keepers as the planlets won't necessarily be just like their parent.