I have my G4 screen timer set to 10 seconds.
The screen lights up for 10 seconds on any voice call - regardless of length of call.
I'm sitting on a slow system right now - 38 talkgroups programmed (system actually has more). Screen is dark, externally powered (charging) - turn the volume knob and the display lights up almost instantly.
On a busier system, during a call, adjusting the volume (even during a voice call), the volume bar shows up fairly quickly.
At other times (I still need to determine), the display is much slower to respond - perhaps when the radio is recording the voice call...
Not a Radio Shack fan.....