The ServiceLevelAgreements and BusinessRules under Admin\HelpDesk is not applicable for ServiceCatalog,infact Business Rules cannot be configured for Service Catalog.
The SLA's for ServiceCatalog have to be configured under Admin\ServiceCatalog on the "Manage" option.
If the Service Request is on "onhold" (or any status with timer stopped)the timer doesn't run and so it wouldn't go overdue
Maljeev
ServiceDesk Plus Support
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http://www.manageengine.com/products/service-desk/support.html