Set safe sun exposure windows by skin type.
A day outdoors is safer managed as a schedule than as a single limit. Shade removes a share of the time entirely, clothing removes a share of the skin, and the remaining exposure is weighted by UV index against a reference of 7 to give a comparable dose figure. Break intervals tighten as the index rises, because at index 8 or above unbroken exposure accumulates a damaging dose within about twenty minutes.
UV-weighted exposure plan
Direct sun minutes = hours x 60 x (1 - shade fraction); weighted dose = direct sun minutes x (1 - clothing coverage/100) x UV / 7; break interval from the UV band
UV damage is cumulative and individual risk varies with skin type, medication and medical history. Follow official UV forecasts and public health guidance; this planner is informational only.
Within a couple of hours either side of solar noon, roughly 11:00 to 15:00 in summer daylight-saving time. That window commonly carries half of the day's total UV.
Generally yes, for the skin it covers. Fabric does not wear off, wash off or get applied too thinly — a tightly woven shirt and a wide-brimmed hat outperform any sunscreen regime.
Far less than most people assume — often ten to thirty minutes on forearms a few times a week in summer. Deliberate prolonged exposure is not required.