(1) In SSRS timeout can be set dataset level inside the report using BIDS/SSDT by navigationg to the dataset => Properties => Query => timeout (in seconds)
(2) In SSRS timeout can be set at report level by selecting the report and navigating to “Manage Processing Options”.
Here in the “Processing Time-out” section, we can select Use site default setting if we want to use the value specified at the report server level. Otherwise, select Do not time out report processing or Limit report processing in seconds if you want to override that value with no time-out or different time-out values.
In case or MOSS 2013 with SSRS 2012 integrated scenario, open central administration for SharePoint and select the SSRS service application and select System Settings.
(3) System Report Timeout defines the server side timeout behavior.
The default report processing timeout value, in seconds, for all reports managed in the report server namespace. This value can be overridden at the report level. If this property is set, the report server attempts to stop the processing of a report when the specified time has expired.We can set it to -1 for unlimited timeout.
(4) In addition there are session level timeouts. The default session timeout is 600 seconds. The RDLX Report timeout indicates the length of time in seconds the report session remains active.
(5) In SharePoint integrated mode the timeout is reduced to 120 seconds. The timeout in SharePoint is actually related to the fact that reports are rendered using the http runtime. This HTTP timeout defined by httpRuntime executionTimeout defined in web.config of both Sharepoint as well as SSRS located at InetPub\wwwroot\wss\virtualdirectories and C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\15\WebServices\Reporting respectively.