[M]illet cultivation was an auxiliary subsistence strategy in Northern China from 10,000 to 7000 BP; while hunting-gathering was the primary subsistence strategy, the earliest millet-cultivation might have emerged in eastern Inner Mongolia post 7700 BP.
Millet cultivation transited from a secondary strategy to become dominant in the Guanzhong area of north-central China during 7000-6000 BP, and probably facilitated the development of early Yangshao culture in the middle reaches of the Yellow River valley.
Intensive millet-based agriculture emerged and widely expanded across the Yellow River valley in northern China during 6000 to 4000 BP. This promoted rapid population growth and cultural evolution in the late Neolithic period, and was key in the subsequent emergence of the ancient Chinese civilization.From here according to studies of archaebotanical evidence.
Note that the dates are BP and not BCE. This represents a much sustained period of proto-farming than is commonly assumed. It would be interesting to know if climate or evolution of millet or something else were more decisive in the transition from proto-farming to farming.