The following time format is not usable with feedgnuplot, but it is fully compatible with gnuplot:
--timefmt '%H:%M:%3.S' for time like this: 16:02:54.672
The perl script terminates because Time::Piece does not support millisecond in the time formats:
http://stackoverflow.com/questions/4012068/how-do-i-parse-microseconds-with-timepiece-strptime