At a startup you might get core technologies going in a month, while at a big tech company the timescale might be closer to years.
I worked at a startup and the focus was on the work. I got to make decisions on what to work with, what technologies to adopt, and then I had to get them running. I worked on core technologies.
At a large company you rarely get to do this. You usually have large systems in production, have very large teams, and get to work on an established code base adding a feature or fixing something.
An interesting exercise at a large company might be to look at the version control checkins from the beginnging. The features at the beginning of the log probably went in a lot faster from fewer contributors.