You can customize your session timeout by making changes in web.xml file. You can refer to this question for details:
In order to hide the session timeout popup, edit the file utilities.js which is present in the location:
In the file, comment out the code that is highlighted in the image below. This code is responsible for the popup which appears showing the session is about to expire or the session has expired. Hence commenting it out the currently open report/dashboard page will continue to be open even if a users session has timed out.:
The code which has to be commented out in utilities.js we are also mentioning below
var i=document.createElement("div");i.id="session-timeout-block",i.classList.add("modal"),i.classList.add("fade"),i.innerHTML='<div class="modal-dialog"><div class="modal-content"><div class="modal-header"><h4 class="modal-title">Session Expired!</h4></div><div class="modal-body"><p>Your session has expired. Please login to continue</p></div><div class="modal-footer"><button type="button" class="btn btn-primary" id="timeout-redirect">OK</button></div></div></div>',document.body.appendChild(i);
Save the file. Your popup will be disabled.