Just to elaborate a bit - I thought there was another question around in the communities asking to add a constant to a timestamp - but my searches keep coming up with this case - so will expand the method here.
Calculation can be done on time objects via XPath
Here is one I have setup : (not quite the same calculation) but :
You can see we create a dummy xml object, and then here I have two unix timestamp objects :
And then a calculation via XPath to gets the delta time :
You can see that the input values are "String" but are then converted to numbers via XPah.
And I store the limittime.result as the timedelta.
So in your case, I'd expect you can do a similar calculation - as per :
https://stackoverflow.com/questions/10411954/convert-windows-timestamp-to-date-using-php-on-a-linux-boxtUnix = tWindow/(10*1000*1000)-11644473600;
From : Convert Windows Timestamp to date using PHP on a Linux Box - Stack Overflow
To give you the unix timestamp from the Microsoft one, and then use the Set Context Variable to get the result value interpreted as a Date/Time field. eg :
Cheers - Mark
PS: If I ever find that original question, about adding an offset to the current time, I will point them here - an offset can be done via the XPath calculation, or it looks an offset can be added in the Set-Context-Variable as well - to add say 600sec for some sort of expiry.