Back in QV9 there was a registry setting for QVS to set a ticket timeout.
I never tested it to for the QV10/11 settings.ini-file, but maybe it still works..
TicketExpireTime defines how long a ticket is valid.
To manipulate the TicketExpireTime you have to add it in the registry at
My Computer\HKEY_LOCAL_MACHINE\SOFTWARE\QlikTech\QlikViewServer\Settings 7
TicketExpireTime should be set in seconds. Default is 600.