The longevity of ylang-ylang's warm, sweet scent on your skin or hair depends on several general factors common to all essential oils. In perfumery terms, ylang-ylang is considered a middle note, meaning its scent tends to be more substantive and lasting than light, top-note oils like citrus or eucalyptus, but it may not linger as long as some deep base notes like sandalwood or patchouli.
More practical factors are at play. Your individual skin chemistry and hair type significantly influence how a fragrance develops and how long it lasts. Oilier skin or hair can sometimes hold scent molecules longer. Crucially, the carrier base you use matters. When diluted in a body oil, the scent will linger on the skin for a few hours, gradually fading. When added to a hair mask or a small amount of leave-in conditioner, the fragrance can cling to hair strands for much longer, even until the next wash, because hair fibers trap scent effectively. The warmth of your body or environment will also cause the scent to diffuse and evolve over time, which is part of the aromatic experience.