in this video: (DCS ORIGINAL ONE)
You can see the HUD having updated inmediatly, you can see each knot that you increase, but real one have a delay (on porpouse???) I am not sure, but I think is around 20ms
here is a old youtube video where you can see that delay in the altitude and speed scale
ofcourse this is old and you will tell is a F16A, but for sure more youtube investigation could bring some light in this