This will be applicable only for specific suppliers. Majority of the suppliers will have standard delivery. For others When you validate your cart, several delivery methods will be proposed to you (one delivery method per supplier).
Please note that the proposed dates are indicative only, and may take into account the shipping time (lead time to ship) indicated in the offer (if configured). Also this will only be applicable if the supplier is offering such an option, delivery schedules will remain as normal if this is not applicable.