Once the youngest baby is about 3 weeks old, you will find that the egg will be pushed aside and they won't need it anymore. You can safely remove it at that time.
Believe me! It's not easy growing up and surviving when you are the smallest baby in a larger clutch of 5. The smallest gets fed exactly the same thing as the oldest and you have to watch that mom isn't feeding undigested whole seed because the oldest one can handle it, while the youngest one could not. When I have a hen that does this, I take away seed and just offer soft food until the smallest one plays catch up in age in abilities to the older ones.
Continue to monitor the little one, as it needs all the advantages it can get!