Use

 (Note: up to Release 3.1H "time-independent conditions" were termed "document conditions"). No validity periods and scales can be defined for these conditions. The conditions in purchase orders are always time-independent. You can determine whether time-dependent or time-independent conditions can be maintained in quotations and scheduling agreements via the document type in Customizing. (<Document> Define document types.)

SAP recommends working with time-dependent conditions for quotations and scheduling agreements, since these provide a wider range of processing options.