If you are using current versions of aciviti
then you can solve your problem by following these approaches:
1 - JAVA API
historyService.createHistoricProcessInstanceQuery()
.finished()
.processDefinitionId("XXX")
.orderByProcessInstanceDuration().desc()
.listPage(0, 10);
2 - REST API
GET history/historic-process-instances
For more details you can follow : activiti user guide