'Multi growing point', to cut or not to cut

[alpiner]

Originally Posted by Robert

where the offshoot emerge from the mother plant, i would made a small incision, wait for roots to form and finally cut and separate it... now u will have another plant...you can trade with me

Thx Robert. Learn something new today. This is great tips for offshoot, without needing to impact mother plant and rooting happens while under care of mother plant. Your 'incision', is it a slit(line), a slice(small area), or a deeper cut(beyond outer layer)? What's the size of the incision? And typically how long does it take for the roots to form from the incision? Sorry, getting carried away with info.
Btw, my N.ventricosa x ramispina has been soaked in water for 3 month without any progress. I did cut a 2-3cm slit at the bottom. Has been a looong wait, no root and shoots, but not rotting.
Anyway, for the companion for these N. Spectabilis, they are still too small to do anything. Assuming they're diff plant from my main, will the fight for root-space and air-space impact the growth?