Question

how the amount and time of secretion of hormones are controlled

Answer 1

All the organisms have an automatic inbuilt feedback mechanism that allows the recognizing cells of the particular glands to recognize the amount of that particular hormone in the  body.
For example, the cells of the pancreas gland recognize if there is less or more blood sugar level in the body. If the amount of blood sugar is less then the insulin stops getting produced for some maltose to get accumulated in the body. However, if there is more  amount of blood sugar then the insulin starts producing more insulin and thus regulates the blood sugar level in the body.