Whose time? Most likely, an agent's, these days, and its operator probably couldn't care less if the agent hand-rolls AES in COBOL as long as it gets the job done, if the job is reverse engineering somebody else's crypto.

The heuristic "don't hand roll your crypto" is just that – a heuristic. Understand why it exists and you get to decide if it makes sense in your scenario or not.

But in this case if they had used a standard AES package it would have saved time and tokens. Just because we have AI doesn't mean that we should encourage it to reinvent every wheel.