IIRC Unix timestamps are measured in seconds since epoch. QlikView uses Excel-timestamps, meaning that the fraction is the time value (0.25 = 1/4 of a day = 6 hours) and the integer part is the number of days since ...(I don't remember)
You may have to divide the Unix timestamp by 86400 to get to the Excel-timestamp.
Now that I think of it, Unix timestamps may also be specified in UTC time, depending on where they come from. The fact that both servers are located in the same timezone doesn't matter, they may still have a different base clock that is converted to local time in a different way. Most Windows servers have a base clock in local time, while Unix machines have a base clock in UTC.
Just a guess, my unix knowledge isn't as fresh as it used to be...