Comment 2 for bug 385810

It's easy to change it to always say 'last downloaded {today|some time ago}', but the code we're using to convert a timedelta into a meaningful string is what's responsible for the '24 hours' bit, and that code is used in tons of other places and behaves just like it was intended to [1], so I'll do the easy change now and leave the other for later.

[1] https://launchpad.canonical.com/PresentingLengthsOfTime