That's about the time I'd expect for a new hire to ramp up on the codebase and submit a PR behind a feature flag and probably experiment that makes it to production. It takes a day to even set up the environment and be able to start looking at and running the code locally. Four days to read through a brand new codebase, identify the changes that are necessary, write a small tech spec (optional based on how small the change is), submit the PRs, get them reviewed and approved, and then merged sounds reasonable to someone who's never worked in the codebase before.