If you look in a modern airliner, the G/S can show up on the ADI at a range of about 20 miles. The green light (Autoland?) kicks in at between 5 and 8 miles, depending on the airport.
For ILS23 at YPAD I get the LAND3 at almost 10 miles, but it is at the same time as I get clearance to land on that runway.
At ILS16 at YMML I get LAND3 at about 5 miles out, the same time get clearance to land.
The pattern is that I always seem to get my LAND3 just as the ATC window opens to inform me that I have clearance to land.
If I tune in the ILS frequency, I get to see the indicator on my ADI from about 20 miles out. I have noticed this on all of my modern airliners, that I have checked it on.
I think that's why it goes to green so far out from the runway.

Mark