String To Time – negative value not working

My goal is to hide elements if their post date is older than 7 days.

I’m trying it with “Post Date” as dynamic tag and want to combine it with String To using conditional value “-7 days”. Unfortunately the result of the conditional value is not as expected a timestamp 7 days in the past but for whatever reason the value “-7”.

If I change the conditional value to “+7 days” I get a wonderful timestamp like “1572189148”. But “-7 days” does not give me a timestamp.

Is it not possible to use negative values or am I doing this wrong?
How can I get my condition to work?

Wonderful plugin btw. It’s very useful for my current project.