When should the Commissioning Authority (CxA) be brought onto the project team?

According to LEED v4, the commissioning authority (CxA) should be contracted before the end of the Design Development (DD) phase and should be involved in the project team from early in the Schematic Design (SD) phase1.

References := LEED v4: Building Design + Construction Guide, LEED v4 -U.S. Green Building Council, SBGD - Part D – ConsultantScopes of Work 3. Commissioning Authority, What’s new in LEED V4 – Commissioning Changes - Steven Winter …, LEED ENHANCED COMMISSIONING | Steps and Downloads