The amount of time a supplier takes to make a delivery is the 'Lead days.' In AIM, you can use modelling to calculate or bulk update 'lead days' for each product / warehouse. Doing so will ensure that the stock limits and replenishment timings are calculated with enough stock on hand to cover the delivery window. 
TIP: If you have a product history, you can update lead days based on how long purchases have taken in the past. Use the 'Use Actuals' option to apply the average past delivery time to each product.