PR without material

Hi,

I created one PR with item 00010 without material(I entered short text),Account assignment K.I entered delivery date as 31.01.2014 and I also entered

Planned Delivery Time in Days as 10(Quantiites/dates tab),then my delivery date will be 10.02.2014 ???.But there will no changes in my delivery date(31.01.2014).There was no calculation .why it is so? Can somebody please advise me,please?

-Regards,