Great! The New Year 2015 starts really fantastic! :-)
I am so grateful for your answer. Strange, that apparently we have to mix up two Modules (Date::Calc and Time::Local) to get it right.

I have to read the manual of Time::Local to fully understand your answer.
Funny that the first timestamp (391265355) gets the wrong daylight savings time.
One moment: May is far into the daylight saving time == 1 ... So it is right. Probably my expected date is wrong hmmmm

I will try to find an answer on myself.

Thank you again :-)

marek