The Yan Emperor is legendary and presumably lived some 5000 years ago. The Hongshan culture (4700 to 2900 BCE) itself is Neolithic. Earlier samples from this culture yielded haplogroups C, N1 and O2a, which are also found in the Mongols. N1 is ancestral to the N1c1 of the Uralic peoples, including the Finns, Saami, Karelians and Estonians in Northeast Europe.
Haplogroup O2a2b1a1-M117 is very widespread around China. It is only found in 10 to 20% of Han Chinese. It is more common among Tibetans and Nepalese (Tamang, Newars) and is also found among Tungusic peoples (such as the Manchu, Evenki, Nanai, Xibo and Oroqen in Northeast China and Siberia), the Mongols, Uyghurs, Laos, Vietnamese, Koreans, Japanese, and even in the Philippines and Indonesia. I wouldn't be surprised if it was one of the main lineages that spread farming from the Yellow River around East Asia during the Neolithic period.
O2a2b1a1-M117 (aka Page23) was formed 17600 years ago, but has a TMRCA of 11300 years. All its immediate subclades (MF1380, M1706, F22770, CTS7634, M1726, A9459) have a coalescence age of 6500 to 6900 years, which corresponds to the Neolithic expansion of farming in China.
The O-F2137 clade (downstream of M1706) was formed 6000 years ago according to Yfull and is apparently found mostly among Han Chinese (Hebei, Jiangsu, Zhejiang, Guangdong).