This node relates twelve and mediation, here is another way other than the Christan perspective of the resident node. In yoga, twelve marks units in time.
For most of our waking and sleeping states thoughts stream constantly in associative tangents. The ability to keep the mind defined on a single point is for the majority of us, shorter than you imagine.
There are units of time in the tradition of yoga for mental stillness.
Concentration is the initial hovering of thought, like a dragonfly above water.
Concentration in this sense is defined as twelve seconds without a break. You can say you were concentrating if your attention can rest for this length of time on a single point.
Twelve consecutive concentrations unbroken have a duration of 2.5 minutes, this can be considered a single meditation upon a point.
Attaining the ability to perform twelve meditations continuously without a break, for the period of half an hour is what the yogis call samadhi.
The units seem small, but participation in the experience will show otherwise.
Source Asasnas 608 yoga poses -Dharma Mitta