public void setServerSessionIdleTime(int idleTime) {
        if (getServerSessionIdleTime() == idleTime) {
            return;
        }
        // Set the new property value
        JiveGlobals.setProperty("xmpp.server.session.idle", Integer.toString(idleTime));

        if (idleTime <= 0 && isMultipleServerConnectionsAllowed() )
        {
            Log.warn("Allowing multiple S2S connections for each domain, without setting a " +
                "maximum idle timeout for these connections, is unrecommended! Either " +
                "set xmpp.server.session.allowmultiple to 'false' or change " +
                "xmpp.server.session.idle to a (large) positive value.");
        }
    }
Returns the number of milliseconds to elapse between clearing of idle server sessions.

@return the number of milliseconds to elapse between clearing of idle server sessions.
xmppserver/src/main/java/org/jivesoftware/openfire/SessionManager.java