I tried an experiment with the Ambient module, running it overnight to see the change in the light level as the Tessel sat beside my window. The Tessel was set to capture results every five minutes, which it did for the most part, but once every 15-20 cycles, it seemed to get stuck and not run for a while. When it did eventually run, it would run the same number of intervals it had missed, causing the same output to be dumped.
Additionally, my method of logging time seems to have had some issue as well. The times are GMT since I didn't do anything with them, but for some reason they only ever range between 6:30am and 7:30am.
Not sure where the issue here lies, and good luck debugging it. I've created a gist with the output, with xxx next to the batch regions.