import type { TimeDurationUnit } from "../../types/index.js";
/**
 * Return true when `unit` is a valid TimeDurationUnit.
 *
 * - Valid units are: "hours", "minutes", "seconds", "milliseconds", "microseconds", "nanoseconds".
 * - Uses type assertion to narrow the type.
 *
 * @param unit string candidate
 * @returns boolean indicating whether the unit is valid
 *
 * @example isValidTimeDurationUnit("hours") // true
 * @example isValidTimeDurationUnit("minutes") // true
 * @example isValidTimeDurationUnit("seconds") // true
 * @example isValidTimeDurationUnit("invalid") // false
 */
export declare const isValidTimeDurationUnit: (unit: string) => unit is TimeDurationUnit;