At about 2 weeks old when their eyes open and they start venturing out of the nest, they will also start to nibble on the food in their environment. Which is why you always want to have a fresh good quality hay(no mold, no noxious weeds, not dusty) that isn't too coarse(has the softer pieces) in there with them. It's the best food for them to help as their digestion adapts to eating solid food. https://flashsplace.webs.com/accidentallitters.htm
Agree, their eyes open between 10-14 days. They will venture out and start nibbling on pellets at about 2 weeks, while continuing to nurse. There is no hard and fast rule on when they stop nursing. It’s basically up to Mom. Usually it’s at least 4 weeks or later.