The team I currently am part of experiences fairly high turnover, with members typically moving to different projects within the same company. Currently our "training" for new members is to pair them with a primary contact (usually the most recent person to complete their training) who will provide them with hands-on experience and will ask more senior developers if the newer hire ask something the mentor doesn't know. It provides a chance for the new hire to get involved quickly, and challenges the mentor to improve his/her understanding of the system also.
However, as you can imagine, this style of training is very time consuming, and doesn't provide a very good knowledge transfer (misconceptions propagate, gaps expand).
I've been tasked with generating documentation and training materials for our future new hires. I already do technical writing occasionally, but it's for the end user and is highly specific with lots of screenshots and consumes a large amount of time to complete.
Creating the new documentation for new hires is considered low priority and I've only currently got ~40 hours to work on it. Documenting the system the current way I write technical documentation would barely scratch the surface in 40 hours. Especially considering I have to document not only about the code base, but also about deployments and support.
How can I quickly write documentation to get new hires up to date as quickly as possible without investing significant time in writing the documentation?
We currently have both a wiki, and some training documentation, however both are kind of sparse.