With probably the majority of NT scholars, Ehrman emphasizes that the exalted claims about Jesus reflected in the NT (e.g., that Jesus shares divine glory, divine rule, the divine name, and is to be given universal reverence) all appeared soon in the aftermath of Jesus’ execution. These convictions were based primarily on experiences of the risen/exalted Jesus (“visions” in Ehrman’s terms) by Jesus’ followers, which conveyed the conviction that God had raised Jesus from death and had uniquely exalted him as Christ and Lord.
Ehrman (rightly in my view) also notes that these lofty claims about Jesus reflected in the NT seem to have erupted very early, so early that they are presupposed as widely shared already by the time Paul wrote his letters (from ca. 50 CE and thereafter). In a commendable example of changing his mind, Ehrman acknowledges that prior to immersing himself in the evidence and scholarly analysis for this book, he had assumed a much slower and more drawn-out process, but was driven to conclude that these remarkable Christological beliefs erupted much earlier and much more fully than he had thought. It’s always reassuring when a scholar admits to learning something new, and even to changing his/her mind.