About which day in a normal human menstrual cycle does rapid secretion of $\text{LH}$ (popularly called $\text{LH}$ -surge) normally occurs?

Both $\text{LH}$ and $\text{FSH}$ attain a peak level in the middle of the cycle (about $14^{\text{th}}$ day). Rapid secretion of $\text{LH}$ leading to its maximum level during the mid-cycle is called $\text{LH}$ surge, which induces rupture of Graafian follicle and thereby the release of ovum (ovulation).