> Or maybe use an available timeserver via document().  But use 
> 2 distinct URLs.
> 
> I.e. 
> document('http://my.timeserver1.com/current-date-time?reason=startup')
> and 
> document('http://my.timeserver1.com/current-date-time?reason=ending')
> 

And don't just put the start time in a variable. Variables are typically
evaluated when they are first used: just because the variable appears
lexically near the start of the stylesheet doesn't mean that it's evaluated
before anything else happens.

Regards,

Michael Kay
http://www.saxonica.com/
http://twitter.com/michaelhkay