Enterprise business modeling efforts will slowly increase in parallel with your enterprise architecture modeling efforts because the architects need to base their work on the needs of the enterprise. When the enterprise architecture stabilizes, efforts will diminish. From that point on, you should update your models as project teams discover deficiencies in them. This often happens because your models don't reflect recent changes within your environment, such as the adoption of new technologies or the introduction of new offerings by your competitors.
On project teams, enterprise business modelers will be involved in the latter part of Inception and throughout Elaboration as they assist, review, and mentor the modeling efforts.