It depends on the system. Usually in polymorphonuclear cells DCFH stands for 30 min and leakcs out of the cell DHE does the same at around 40 min. In other cell types, endotelial cells, both stays 10 min longer.

Good luck

Thank you Juan and Shiv Kumar for your answers. The cells are CHO, the concentration of the stain 25 µM, after exposure to the stain, the cells will be protected from light until confocal microscopy.