In QMC->System->Setup->QlikView Servers->Your QVS->Documents->Server, set the Document Timeout to a lower value.
Remember that whenever a document gets thrown out of server memory, the first user that reopens a document will face an additional delay because that document must be reloaded into RAM. If your documents are many but all reasonably small, nobody will notice. If your documents are few but very large, this delay will become annoying.
