This process is applicable when an item has the following planning attributes:

• The item must have a setting of make, purchase, or transfer to order. This setting does not currently work when the item has a stock status.
• Requirement planning must be daily buckets not weekly buckets including within the planned order horizon. Please contact support if your account does not have the hidden daily buckets setting enabled. 
• There is an open customer order, forecast, or dependent demand requirement to fulfill outside of the items lead time.
• There is a CRT (customer response time) value for the item that is not 0. The CRT is the value used for the order buffer and is found in the options tab within the Planning Settings section.

In the example below, the item is purchase to order with a total lead time of 5 days and a CRT of 0 days.  As can be seen, since the item has inventory, the suggested order at the point where there is not enough inventory, are one to one where the replenishment is due on the same day as the requirement.

Now, we add 2 days as the CRT value for the item.

What happens now is that the replenishment order is scheduled to arrive two days before the order requirement is due.

Please note, that if the buffer falls on a weekend or during the lead time, the offset requirement is scheduled around the non-delivery period but after the lead time. That is why on the 23rd of January, there is a total replenishment of 13,680 due to arrive to fulfill the requirements dueing on the 24th and 25th of January.