Source code for the timestamping applications is supplied in the onload-examples subpackage. After installing the subpackage, it is available in:
/usr/share/doc/onload/examples/onload/hwtimestamping
The source code is not compiled as part of the Onload install process. To build it do the following:
# cd /usr/share/doc/onload/examples/onload/hwtimestamping
# make