Declarative framework enabling to determine conditions employed in a decision support systems aimed at small and medium size enterprises involved in a unique, multi project-like and mass customized oriented production is discussed. The unique production orders grouped into the set of portfolio orders is considered. To each production order treated as an activity network of common shared resources, known in advance, however by nature imprecise operation times are allotted. The problem concerns of scheduling of a newly inserted projects portfolio taking into account imprecise operations imposed by a multi–project environment. The answer sought is: Whether a given portfolio can be completed within assumed time period in a manufacturing system in hand? The goal is to provide a declarative model enabling to state a constraint satisfaction problem aimed at multi project-like and mass customized oriented production scheduling. The attached calculation example illustrates the computational efficiency of the proposed solution.