In v. 0.23:

• trigger is set to poll url contents every minute [1]
• log is updated every minute [2]
• when the polled URL [3] changes, it takes many iterations before URLTrigger reports the change and triggers the build. In the build list for [1], see build #246, where the url changed and someone built the job manually on Aug 1, 2012 5:14:43 PM. URLTrigger did not trigger the build until Aug 1, 2012 5:25:20 PM (#247). For build #248, it's two hours after the url has changed, and URLTrigger still hasn't triggered the build.

[1] https://ci.lille.inria.fr/pharo/view/Pharo%202.0/job/Pharo-2.0/configure
[2] https://ci.lille.inria.fr/pharo/view/Pharo%202.0/job/Pharo-2.0/urltriggerPollLog/?
[3] http://pharo.gforge.inria.fr/updates/pharo2.0/updates20.list