Session break timeout can be changed by two methods:
In system registry settings for BI server set required value of the TimeoutSec parameter in the System/Session subsection.
To keep BI server connection active, call periodically the following code on the HTML page: Metabase.getStatus, for example:
setInterval(function () {metabase.getStatus()}, 1000);
See also:
Questions and Answers | Metabase.getStatus | System Registry Settings