/**
 * Return true when `value1` is strictly before `value2` for PlainTime values.
 *
 * - Uses Temporal.PlainTime.compare to compare times.
 * - Returns false if either input is invalid.
 *
 * @param value1 ISO PlainTime string for the first value
 * @param value2 ISO PlainTime string for the second value
 * @returns boolean indicating whether value1 < value2
 *
 * @example isBeforeTime("12:34:56", "13:34:56") // true
 * @example isBeforeTime("12:34:56", "12:34:56") // false
 * @example isBeforeTime("13:34:56", "12:34:56") // false
 * @example isBeforeTime("invalid", "12:34:56") // false
 * @example isBeforeTime("12:34:56", "invalid") // false
 */
export declare function isBeforeTime(value1: string, value2: string): boolean;