They can show up fairly quickly, as the primary and secondary metabolites break down, but the more important fact that a lot of people seem to ignore is that if they show up soon after ingestion, there will ALSO be those other metabolites present.
That's why they said there was no evidence of subsequent use - because he was being periodically tested during that time, and these tertiary metabolites were showing up, suddenly, where they weren't showing up previously, without any of the earlier "generation" metabolites ever showing up.