difference between an integer and current-dateTime()

Hi all,
    I've got a number 1585039138 for example (which is number of seconds
since epoch 1970-01-01T00:00:00Z UTC). I wish to find the duration (in
minutes or seconds) between previous number and current-dateTime(). I wish
to do this with XSLT (2/3 both are fine with me, preferably non schema
aware). I expect this difference to be always positive, since the number
will change depending on what moment (at any moment, I wish to find this
difference) it is calculated. How can I do that?


-- 
Regards,
Mukul Gandhi