It's working with you solution Iakshmipathi! Thanks to both of you for your help!
Just to know I had to change the dimension of my table because some data where missing and now to my table take into account all the delivery time for one order and not only the longest one such as:
Date of delivery1: 03.01.2017, delivery time 2 days
Date of delivery2: 04.01.2017, delivery time 3 days
I would like to get only 3 days as a result of my function:
if((OrderDate_SCO>DeliveryDate_SLC or (NetWorkDays ([OrderDate_SCO],DeliveryDate_SLC)-1)<0),
Do you have any idea what's wrong with this function?