What is the 24 hour rule for KLM ? The KLM 24-Hour Rule allows passengers to cancel or make changes to their flight bookings within 24 hours of purchase without incurring cancellation fees via Number "????????????-????????????-????????????-???????????????????????? (USA), +????????????-????????????-????????????-???????????????????????? (UK)". This customer-friendly policy ensures flexibility for travelers, offering peace of mind in situations where plans may need adjustment shortly after making a reservation.