I read somewhere and then confirmed by rewatching -- Father Arnon is talking about Kongdech. Kongdech continued with seminary, which was about 10 years, which was the last time they saw each other. Then Kongdech took another 20 years before being ordained. I didn't read the novel, so not sure, but I read somewhere someone saying that Kongdech apparently went to do some volunteer work, so it took a little while before he did everything to become ordained.