Slightly literary/news register. Most often appears in fixed chunks like
如约而至 (rú yuē ér zhì, 'arrived as promised', often used poetically for the seasons or weather) and
如约举行 (held as scheduled). For everyday speech,
按时 (ànshí, 'on time') or
按约定 (àn yuēdìng, 'as agreed') are more natural.
