Sounds like the glow plug relay is doing its job. The warmer the engine, the shorter the WTS (wait to start) light interval is. Just because the light doesn't come on doesn't mean the GP (glow plug) relay isn't cycling, just that it's OK to crank it. The relay senses the resistance of the GPs which varies with temperature, and will cycle them until combustion warms them up enough that they're not needed.
Are you having starting trouble, or does it start OK?