Hello! First time chicken mom here, so I always have questions as they continue to grow! My ladies are 19 weeks, and I've read mixed things on when to start offering oyster shells. Some day start at 16 weeks, others say not until they start laying. I decided to split the middle, and put some out for free choice in the run today. They are eating it like crazy! Is this okay? Should I not be offering it free choice at this point? I've had it put for like 10 minutes, and it's constantly crowded with chickens going back every few minutes. Thank you!