HI , for 9508 it is possible go to phone set and change inactivity timer .
For 9608 it is possible change 46xxsettings.txt
17.7.8 Inactivity Timer (Auto Return)
You can set a timer which will return the phone to its normal call display after a set period of phone inactivity. By default
the phone will be set to auto return after 60 seconds.
Note that the timer is not applied to all menus. For example it is not applied to the A-menu and to the visual voice menu.
It is also not applied to the System Admin section of the Features menus.
1. Press the Features soft key if shown. To do this during a call, press the PHONE key and then press the
Features soft key.
2.Use the up and down arrow keys to highlight Phone User. Press Select.
3.Use the up and down arrow keys to highlight Phone Screen Settings. Press Select.
4.Use the up and down arrow keys to scroll the display to the option Auto Return (s).
5.Press Change to change the setting.
· Disabled
Do not use the inactivity timer.
· 30 / 60
Apply the inactivity timer after the selected number of seconds.
############### DISPLAY BACKLIGHT CONTROL ################
##
## Idle Time Before Turning Off Backlight (minutes)
## Number of minutes without phone activity to wait
## before turning off backlight. A value of 0 means the
## backlight is never turned off. This parameter is
## supported only by phones which have a backlight.
## The default is 120 minutes.
SET BAKLIGHTOFF 1