In practice, an individual FDES takes 6 to 9 months, in three steps: collecting LCA data from your suppliers (modules A1-A2, often the longest phase), LCA modelling by an accredited body, and third-party verification. Lead times lengthen if your upstream suppliers do not have structured environmental data of their own, so allow a buffer of 2 to 3 additional months for complex supply chains.
Read the source article: EPD or FDES for France: which to publish, and at what cost?