For anything non-trivial, as your code grows the amount of time required to understand it will grow too -- even if you're using "standard" frameworks, etc. -- because the business logic driving your design decisions is learned with experience. For example, we have a guy at our large company who's a terrible programmer but we keep him on the team (albeit somewhat quarantined) because he's been there forever and has enough institutional knowledge to be valuable.

As your systems grow even more, there will not be off-the-shelf solutions. You'll have to sit down and do some real-life architecting and that won't be learned in 2 weeks. Even if you could perfectly document all your systems and design intentions (you can't), well documented decisions still take time to be read and "soak in".