It depends on many factors: Your requeriments, the maca colour, and the type of maca you try. Here the scientific information:

According Acceptability, Safety, and Efficacy of Oral Administration of Extracts of Black or Red Maca (Lepidium meyenii) in Adult Human Subjects: A Randomized, Double-Blind, Placebo-Controlled Study (a). The study demonstrated that consumption of a spray-dried extract of red and black maca for 12 weeks resulted in an improvement of mood, energy, and health status, and a reduced CMS score.

According Effect of Lepidium Meyenii (MACA) on Sexual Desire and Its Absent Relationship With Serum Testosterone Levels in Adult Healthy Men study. (b), an improvement in sexual desire was observed with Gelatinized Maca since 8 weeks of treatment.

Acording A Pilot Investigation Into the Effect of Maca Supplementation on Physical Activity and Sexual Desire in Sportsmen study (c), an significantly improved the self-rated sexual desire score was observed with 2 weeks Maca extract supplementation.

According Maca Reduces Blood Pressure and Depression, in a Pilot Study in Postmenopausal Women study (d), significant decreases in diastolic blood pressure and depression were apparent after Maca powder treatment for 6 weeks.