When do the times for the morning and evening adhkār, and the adhkār for waking and sleeping begin, and is it obligatory to say the morning adhkār for one who woke up for Fajr prayer and then went back to sleep?

The time for morning remembrances (adhkar) begins at dawn and ends at noon. The time for evening remembrances begins when the sun declines (after noon) and lasts until midnight. However, the closer the time of remembrance is to dawn for morning adhkar, or to evening for evening adhkar, the better. There are also remembrances tied to specific times, such as the night remembrances after sunset. Many scholars are of the opinion that the time for morning remembrances is between dawn and sunrise, and the time for evening remembrances is between the Asr prayer (afternoon) and sunset. Remembrances upon waking begin when one rises from sleep, and remembrances before sleep begin when one lies down on their bed. If you wake up for the Fajr prayer and wish to return to sleep, it is better to recite the remembrances before sleeping again. If you omit the remembrances, there is no sin upon you, as they are a Sunnah (recommended practice) and not obligatory.