I juggle between various codebases regularly, some written by me and some not, often come back to things after not even months but years, and in my experience there's very little difference in coming back to a codebase after 6 months or after a week.

The hard part is to gain familiarity with the project's coding style and high level structure (the "intuition" of where to expect what you're looking for) and this is something that comes back to you with relative ease if you had already put that effort in the past - like a song you used to have memorized in the past, but couldn't recall it now after all these years until you heard the first verse somewhere. And of course, memorizing songs you wrote yourself is much easier, it just kinda happens on its own.