Countdown Timer / Slot Hold for Collins

During high-demand periods, multiple customers often select the same time slot simultaneously. Collins currently shows nearby slot options even when only one actual space is available, which leads to situations where two customers proceed to payment at the same time. Only one booking is generated, but both payments may be taken, creating refund and service issues.

The request is to introduce a visible countdown timer and temporary hold window when a customer selects a slot, similar to existing behaviour in Tonic. While the timer is active, the slot should not appear available to other customers. If payment is not completed before the timer expires, the slot is released back into availability.