1.) if Idle Client Timeout field is blank,
a.) then normal idle clients (clients that are connected but not doing anything) will never be disconnected
b.) if a client is not connected (connection was lost), then the server will disconnect them after 10 mins (default). The 10 mins can only be changed by enabler file EnabTIME, where syntax is specified in minutes.

2.) if you fill in Idle Client Timeout field, then it will apply to normal idle clients (clients that are connected but not doing anything)

More info here:
http://hansamanuals.com/main/mailnumber___61036/theconf___602/manuals/version___85/english/hwconvindex.htm?shortcode=HW0107SETTINGS_Optional_Features_Options_Card