If you look at my list of activities earlier in the thread, you'll see plenty of things that you could be doing that would fill an 8 hour working day. You certainly wouldn't be spending most (or any) of the day writing about things you already did. You'd be writing documents to specify what is going to happen, or at least what you would like to happen (before the programmers, artists, producers, and everyone else read the document and negotiate with you on the contents). It is entirely about communication - ensuring that your document is adequate for programmers and artists to work from.
But you'd also spend a lot of time, at least once proper development starts, actually putting things into the engine. That's where learning the tools comes in.
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This is a level 5 college degree in the UK, I have somewhat of a portfolio...then what?
I would recommend applying for game design jobs. I also recommend you start looking NOW at what they ask for in those jobs, so that you can spend the next year ensuring that your college work counts towards that, where possible, and where it's not possible, you can do work in your spare time to fill the gaps. You don't need to ask us what you need to be learning - the job descriptions tell you, right from the horses' mouths. Even senior designer job ads are useful to look at because while you can't be expected to have everything on that list, you can be confident that anything on there is relevant to you, and is therefore something to pursue.
I don't recommend even thinking about Q.A. It's a bit of an old cliché for people to say that you get into games by starting at Q.A. and working your way up, but while that is definitely a route for some people, it's not as common today for several reasons - Q.A. teams are smaller than before, Q.A. teams are often off-site and/or outsourced, there are people training specifically in design who might have more relevant skills than Q.A. workers and who are thus more likely to get hired than you, etc. Besides which, Q.A. is an important role in its own right with its own set of skills, and isn't just something that a designer-in-waiting can do automatically.