Don't worry, though. I work with "C++ experts" who don't realize you have to allocate memory before writing to it. Knowing how to program is not a prerequisite to all programming jobs.
You can't devote even 2% of that time to building a portfolio and helping possible future employers to evaluate your skills?
I think this really depends on the position you are trying to fill. A track record of shipping code to customers counts for a lot more in my eyes than open source code (unless we're talking about something really high profile like Firefox or llvm). A lot of really talented and passionate developers are plenty challenged and stimulated at work that they don't feel the need to work on hobby projects in their spare time. What could these people write in one hour that would be of significance?
Next year, you have a better job elsewhere.
There are firms that actively ask people NOT to post code outside (citing IPR); and at times, even go ahead and mention that anything a person on it's payroll writes (even if written in leisure time or at home off work), belongs to the firm. The 'extended workplace' clause in terms of contract could be suitably flexed.