smiller,
Perfectly normal.
According to the BERU link I posted above, the entire glow plug cycle takes 2-5 seconds.
So, you turn the key, and by the time you've focused on the glow plug symbol, some of that
2-5 seconds is already gone.
If your battery has full voltage available, the entire glow plug cycle is just the blink of an eye.
About the time you see it, it will go out.
When the battery voltage is low, it may take longer for the glow plugs to cycle, and it may take a while
longer for the engine to start since it will not spin over on the starter as fast.
Hope this helps,
Roger