Once the plant has about 3/4 brances and they have 3/4 nodes on then you can take cutting.i have taken cutting when the plant has just 2 nodes but this was a desperate messure.you can get a few cutting when the plants are about 3/6 ince but i wouldnt advise it wait till it's about a foot tall.
now then, ive just took 10 cutting of 7 ov me girls they r lookin ok but some part ov them stem leaves r a purple colour, do u know wots this is dwon 2? i av them in humid dome with a heat mat underneath