In #pywikipediabot today, Pyfisch pointed out that User.contributions and Page.getVersionHistory are returning the MediaWiki timestamp format (example: 20130427104527). I've gone ahead and modified both methods to return pywikibot.Timestamp formats, which are much easier to use.
I've noted this in the README-conversion.txt file, since this is a breaking change from trunk.

I doubt these two are the only methods that needed changing, so I will try and convert everything else over soon.
-- Legoktm