Hi Dabele

First of all, when it comes to Calendar generation, this needs to be done preferably when fewer to no users interact with the system as there could be performance issues. Further longer the generation, the higher the time taken by the system. Otherwise, how long will depend on business requirements of sales, Procurement, scheduling, and business planning divisions.
 

Further, As per the standard functionality, a recalculation of Planned Receipt Date based on Planned Delivery Date and all different lead-time components is made during the calendar generation. If the calculated Planned Receipt Date is different than the one saved on the line, an update will be made. However, this is not registered in the history log due to performance reasons, since regenerating a calendar usually causes a lot of updates throughout the entire system. But when manually updating the Planned Receipt Date for a PO line, there will be an entry in the history.

For example, let’s say we are going to make 28th of December (12-28-2021) a holiday. So, all the deliveries scheduled to be received on that day have to be rescheduled to the next working day.

In this case, system identifies the POs that are to be received on 28th and 31st (next working day). Now, with the calendar regeneration, the receipts belong to 28th are going to add up with the receipts of 31st automatically.  After the calendar regeneration is done, the postponed purchase order lines have the planned receipt date as 12-31-2021.

So, depending on the priorities of the business, it is required to amend and confirm the POs manually.