Polling must die:
Unfortunately, Jenkins has this weird behavior to skip polling while in quiet-down mode.
Since anyone implementing post-commit hooks (as described e.g. on https://wiki.jenkins-ci.org/display/JENKINS/Subversion+Plugin for Subversion) will only perform actual polling very rarely, if at all.
However, whenever Jenkins is quieting down (which can be for a number of reasons), polling is skipped and any post-commit notification, if implemented in terms of triggering polling, effectively discarded.
For less active projects (few commits) this can result in builds being hours, to weeks, late, if at all.
This behavior should be changed to not skip polling while quieting down. The affected projects can start building when Jenkins leaves quiet-down mode. And since Jenkins preserves the queue when shutting down, the affected projects can be built immediately after restart if that's the motivation for quieting down.