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The periodic trigger will trigger a build at every interval you specify. The trigger can run every x amount of days, hours or minutes.
Periodic
Interval
The time interval between triggers.
Start Trigger
When to run first or next trigger.
Trigger Start
The date and time of the start of the trigger.
Associate Changesets
Associate only the latest changeset from all repositories, or associate all changesets from all repositories that have been committed since the last successful build.