I don't follow what you're implying here, sorry?
> How about a 4-5 hours coding rush in the office, where you have to add a few functions or features to an existing codebase?
I work at a company where we actively keep a small set of tasks groomed for new hires. It's extremely difficult to keep a set of meaningful actually-in-the-codebase problems groomed at all times and totally infeasible that the person will spend less than a day coming up to speed on the infrastructure etc. The overhead of doing that is really prohibitive from an interview perspective.
I do think that for the most part, the coding problems need to be synthetic, then, not an active need in your codebase. I am definitely a believer in longer more open-ended coding challenges than 45 minute white board jams though.