Dear behrooz
hi(salam)
this is depend on the complexity of the part and the 3d requirement.because some designer like to model the part and mold fully 3d but some else like to model the part and parting surface of the mold in 3d.so that is very hard to response to your question.the skill of the designer and the cad/cam software that u use is another important factor.
but now i can give u a rough estimation min 3 hours and max two weeks.if u need more information let me know.
be happy
bye
(khoda negahdar)