I've split Execution time into Connection time and Response time.
From now all, when viewing cron jobs' logs, you will see these two values.
For example, here's part of my logs for URL http://www.setcronjob.com/
Last execution time : Wed, 02 Sep 2009 11:45:08 UTC
Connection time : 0.0144
Response time : 0.000835
HTTP/1.1 200 OK
Date: Wed, 02 Sep 2009 11:45:08 GMT
Content-Type: text/html; charset=UTF-8
At SetCronJob, the max connection time is 3 seconds, and max response time is 2 seconds.