When do the times for morning and evening adhkar begin and end?

The morning begins from the last half of the night until the sun's decline (zenith), and the evening begins from the sun's decline until the start of the last half of the night. The best time for morning remembrances (adhkar al-sabah) is after Fajr prayer until sunrise, and for evening remembrances (adhkar al-masaa') it is between Asr prayer and sunset.