Adding Time to a variable

Dear Community, 

I am having a report which gives me as collums the Manager Receipt Time and as well the Epoch time.
For Epoch Time I use a varaible which calculates the time difference between the two timestamps (MRT and 01/01/1970/...).

So far so good, when I get the report both collums are populated in the excel, but beween the MRT and EPOCh I do have an Off-Set of one hour.
For Example:
when I do convert this MRT: Jun 22 2017 13:28:51 in to Epoc it is: 1498130931
But in the Report export to excel it is : 1498134531.621
And when I do convert this in MRT again it is: Thursday, June 22, 2017 14:28:51.621

 

So as you can see there is something off, and this should have something to do with timezone, but I don't know currently how can I add/substract 3600s to/from the EPOCH so it correctly shown in the excel export?
Or am I doing something wrong allready from the beginning?

Thanks for your help best regards,
Stephan