Question

When did the rate of respiration more than the rate of photosynthesis

Answer 1

This is similar to a situation where expenses are more than income. Exactly what happens when animal body doesn't get enough food for energy synthesis is what will happen in plants.
Photosynthesis is an anabolic pathway. Carbon dioxide from the atmosphere and water from soil get converted to glucose in plants in the presence of sunlight. This glucose acts as food in plants.
Respiration is a catabolic pathway. The glucose breaks down into carbon dioxide and water by using oxygen to release energy. This process is similar to the process of digestion in animals where a complex molecule is broken down into simple molecules.
Now, in a case of prolonged fasting in man the body doesn't get proper food and thus no nutrients are provided to it. To compensate this loss the carbohydrates, fats and proteins in the body start breaking down into their simpler forms.
Something similar happens in plants. When the rate of respiration is more than the rate of photosynthesis, the biomolecules present in plants break down to compensate the reduced rate of photosynthesis. This results in loss of dry weight of the plant.

Answer 2

during night time rate of respiration is more than rate of photosynthesis