Siebel RCR are workflows that run at a specified time.
In Siebel using RCR one can specify when to run the workflow and for which record workflow should be run. There is no user action or event required to trigger RCR.
Along with the time when workflow should be run, search spec of primary buscomp of workflow's BO can be provided. Siebel server then executes that workflow for all those records which satisfies the search spec at the given time.
Hope it helps, feel free to ask any questions you may have.