Handle time better / localize time

[tahnok]

--when takes timestamps and assumes they are in UTC, partly because I always set the time on the ring in utc.

The problem with this is that the timestamps printed are in UTC (which is confusing but should be easy to fix). The other problem is that when you don't get a coherent picture when you ask for the data for "today". This may go away with the #14 implementation, but... maybe we can set the time on the ring in local time? Or notice if the date falls between days and issue 2 requests for data?