It appears that the --intervals flag outputs UTC rather than local timezone. This in itself isn't a problem, but it should be documented if it is intended like this.
For example, i just ran the command:
> arbtt-stats --intervals Program:firefox Program:firefox | 08/30/15 11:54:23 | 08/30/15 12:06:23 | 13m00s Program:firefox | 08/30/15 12:51:24 | 08/30/15 12:54:24 | 4m00s Program:firefox | 08/30/15 12:58:42 | 08/30/15 12:59:42 | 2m00s
my local time is 15:01 (13:01 UTC +02:00 CEST) right now, and those are the intervals from just a few minutes ago.
Again: is this intentional or could it be related to something in my setup?