The duration varies based on the concern.

Just like with prescription drugs, some Chinese herbs can do the job after a few doses, while others are taken for months or longer. For quickly onset concerns like a cold, Chinese medicines can work very fast and take effect within hours. For concerns that are chronic or larger in scope like cholesterol, skin conditions and fertility  it can take longer to see results.

FERTILITY and skin conditions CAN BE IMPROVED IN 3-4 MONTHS

A meta analysis study has suggested that management of female infertility with Chinese Herbal Medicine can improve pregnancy rates 2-fold within a 4 month period compared with Western medical fertility drug therapy or IVF. Assessment of the quality of the menstrual cycle, integral to Traditional Chinese Medicine diagnosis, appears to be fundamental to successful treatment of female infertility. 

Ried, K. and Stuart, K. (2011) 'Efficacy of traditional chinese herbal medicine in the management of female infertility: A systematic review'. Complement Ther Med, 19(6), pp. 319-331.

A dermatology study researching patients aged 5–25 years with moderate-to-severe atopic dermatitis were randomised to receive a 12-week treatment. Two hundred and seventy-five patients were recruited. It was found that a herbal formula was effective in decreasing the severity of the disease and improving the quality of life in patients after that time.

Liua, J. Wub, D. Oub, A. et al (2015) ' 'Efficacy of a Chinese herbal medicine for the treatment of atopic dermatitis: A randomised controlled study'  Complementary Therapies in Medicine Vol 23, p644-651