Laying too many eggs can potentially be harmful to hens, as it can lead to various health issues and complications. While egg laying is a natural behavior for hens, excessive egg production can strain their bodies and deplete their calcium and other essential nutrients. Some potential health problems associated with excessive egg laying in hens include:

1. **Calcium Deficiency:** Egg production requires a significant amount of calcium, which is obtained from the hen's diet and stored in her bones. Continuous egg laying can deplete the hen's calcium reserves, leading to weak or brittle bones, eggshell abnormalities, and increased risk of fractures.

2. **Reproductive Disorders:** Excessive egg laying can increase the risk of reproductive disorders such as egg binding, where an egg becomes stuck in the hen's reproductive tract, leading to discomfort, infection, and potential health complications.

3. **Stress and Exhaustion:** Constant egg laying can be physically and emotionally taxing for hens, leading to stress, fatigue, and decreased overall health and well-being.

To help prevent potential health issues associated with excessive egg laying, it's essential to provide hens with a balanced diet, including adequate calcium supplementation, and ensure they have access to a comfortable and stress-free environment.

Regarding the second part of your question, the duration for hens to start laying again after they have stopped producing eggs can vary depending on various factors such as the age and breed of the hen, environmental conditions, diet, and overall health status.

In general, hens typically go through a molting period once a year, during which they shed their old feathers and regrow new ones. Molting is a natural process that can temporarily disrupt egg production, and hens may stop laying eggs during this time. Once the molting period is complete and the new feathers have grown in, hens will typically resume laying eggs.

The duration of the molting period can vary, but it usually lasts several weeks to a few months. After molting, hens may take some time to readjust and resume regular egg production. Providing hens with a nutritious diet, proper housing, and optimal environmental conditions can help support healthy egg laying and encourage hens to resume laying eggs more quickly after molting.