A short video on this (<5min) is available in our videos section:
http://oxygenxml.com/demo/XSLT_Profiling.html

Best Regards,
George
--
George Cristian Bina
<oXygen/> XML Editor, Schema Editor and XSLT Editor/Debugger
http://www.oxygenxml.com

Order of evaluation is undefined in XSLT, and there is no guarantee
that $start is evaluated before the apply-templates call is evaluated.

Yikes!

So how do I write the XSLT program so that it is guaranteed that $start will be evaluated before the apply-templates call is evaluated?

There is no guaranteed-portable way of doing this. Doing an xsl:message that references $start before the apply-templates call would increase your chances; but there's still no guarantee that $start won't be evaluated much earlier, e.g. at compile time.

A safer way to get timing information with Saxon is to use a TraceListener. This is what the Saxon profiler (command line option -TP) does.

Michael Kay
Saxonica