When I first started looking into this, I thought the task will be quite straight forward and all I would have to do was edit the httpd.conf file CustomLog line for the common log, which is used for access logging. I was wrong on this one. After editing this file and restarting, the access log output didn't change.
The thing that I forgot to take into account was that all our services run over SSL, which meant that the access log configuration in httpd.conf is not used! So with this in mind, I opened up the ssl.conf file and found my VirtualHost configuration.
The config file is in: $ORACLE_HOME/Apache/Apache/conf/ssl.conf
In the "General setup for the virtual host", I found a TransferLog line, which I changed to the LogFormat and CustomLog lines instead as per below. The %D parameter logs the time to serve the request.
After a restart, the access log started showing me the request times as expected.
The only catch here is that the request times are in whole seconds, there is no sub-second precision. Apache 2.x has an option to output the microseconds elapsed, sadly this was not available in 1.3.