Gnuplot plots incorrect time for time series plot

I'm printing a time series that has the following format

> 1400536853 0.011955 
> 1400537188 0.013695 
> 1400537530 0.010797  
> ....
> 1400621709 0.010688 
> 1400622023 0.007209 
> 1400622338 0.006685 
> 1400622653 0.005539

The first column is a timestamp in unix epoch format and the second is a variable to plot. Notice that the timestamp pf the first line corresponds to "Tue May 20 00:00:53 CEST 2014" and the last line to "Tue May 20 23:50:53 CEST 2014". I veridied this with the following command:

date -d @<timestamp>

I'm using the following script to plot the time series

set xdata time
set timefmt '%s'
set format x '%H'
plot 'series.txt' using 1:2 with lines notitle

But I'm getting a plot with hours in the range 22, 00, 02. ...22 as shown in the next figure:

I will appreciate any suggestion on how to fix this. May this has to do with not setting properly the timezone? Many thanks in advance

Gnuplot cannot change the time zone and uses UTC for all time data. This is where your 2h shift comes from:

$ date -u -d @1400536853
Mo 19. Mai 22:00:53 UTC 2014

In your specific case, you can just add the two hours in the using statement:

set xdata time
set timefmt '%s'
set format x '%H'
plot 'series.txt' using ($1 + 2*60*60):2 with lines notitle

Beware, that this explicitely assumes, that you run the script only on computers in the same time zone. I think there is no generic way to convert between time zones within gnuplot, since it doesn't support them.