Singling out a particular time for remembering Allah or sending blessings upon the Prophet (peace and blessings of Allah be upon him) may take one of the following two forms:

1. Doing it thinking that there is some virtue in doing acts of worship at this particular time. This is not prescribed except in cases where it is proven that singling out this time is prescribed in Islam.
2. Doing acts of worship at this time but not because one thinks that there is any particular virtue in doing it at this time; rather the time is singled out because one is free and has energy, and so on. There is nothing wrong with this. The earlier and later generations always set out times for studying, reviewing, memorising and teaching according to what suited their situation and the situation of those who were learning from them. This is what people usually do when choosing and singling out times. But there are some followers of innovation who choose a particular time, or a particular number of times to repeat (a word or action), or a particular way of doing something that is not prescribed in Islam. The scholars regard this as a kind of innovation.

Ash-Shatibi (may Allah have mercy on him) said: Innovation (bid‘ah) is a word that refers to a way (of worship) that has been introduced into Islam; it may appear similar to what is prescribed in shariah (Islamic law) and the aim of doing it is to show extra devotion in worshipping Allah… this includes adhering to certain ways and manners (of worship), such as reciting dhikr in unison, taking the day of the Prophet’s (peace and  blessings of Allah be upon him) birth as a festival, and so on.

It also includes adhering to specific acts of worship at specific times that are not prescribed in shariah, such as always fasting on the fifteenth of Sha‘ban (an-nisf min Sha‘ban) and spending that night in prayer. End quote from al-I‘tisam.

The times that it is prescribed in Islam to single out for dhikr include the period between Fajr (early morning) prayer and sunrise, and the period between ‘Asr and sunset, because Allah, may He be exalted, says (interpretation of the meaning):

“... and glorify the praises of your Lord before the rising of the sun, and before its setting.”

[20:130]

“And remember your Lord by your tongue and within yourself, humbly and with fear without loudness in words in the mornings, and in the afternoons.”

[7:205]

The word translated here as afternoon refers to the period between ‘Asr and Maghrib.

And Allah, may He be glorified, says (interpretation of the meaning):

“So glorify Allah (above all that (evil) they associate with Him (O believers)), when you come up to the evening (i.e. offer the (Maghrib) sunset and (‘Isha) night prayers), and when you enter the morning (i.e., offer the (Fajr) morning prayer).

And His is all the praises and thanks in the heavens and the earth, and (glorify Him) in the afternoon (i.e. offer ‘Asr prayer) and when you come up to the time, when the day begins to decline (i.e., offer Zuhr/noon prayer).”

[30:17-18].

Muslim narrated from Jabir ibn Samurah that when the Prophet (peace and blessings of Allah be upon him) had prayed Fajr, he would sit in the place where he had prayed until the sun had risen properly.

At-Tirmidhi narrated that Anas ibn Malik (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings of Allah be upon him) said: “Whoever prays Fajr in congregation then sits remembering Allah until the sun has risen, then prays two rak‘ahs (units of prayer), will have a reward like that of Hajj and ‘Umrah (major and minor pilgrimage).” The Messenger of Allah (peace and blessings of Allah be upon him) said: “Complete, complete, complete.”

Ibn al-Qayyim (may Allah have mercy on him) said: Chapter on remembering Allah (dhikr) at the two ends of the day (as mentioned in 11:114), which are the times between Fajr and sunrise, and between ‘Asr and Maghrib. Allah, may He be glorified and exalted, says (what means):

“O you who believe! Remember Allah with much remembrance. And glorify His praises morning and afternoon.”

[33:41-42]

The “afternoon”: al-Jawhari said: This is the time after ‘Asr until Maghrib. And Allah, may He be exalted, says (interpretation of the meaning):

“... and glorify the praises of your Lord in the ‘ashiy (i.e. the time period after the mid-noon till sunset) and in the ibkar (i.e. the time period from early morning or sunrise till before mid-noon).”

[40:55]

The ibkar is the beginning of the day and the ‘ashiy is the end of the day. And Allah, may He be exalted, says (interpretation of the meaning):

“... and glorify the praises of your Lord before the rising of the sun, and before its setting.”

[20:130]

This interpretation is what is mentioned in the hadeeths (reports) about saying such and such in the morning and evening. What is meant is before the sun rises and before it sets. Therefore, the time for these adhkar is after Fajr and after ‘Asr. End quote from al-Wabil as-Sayyib.

Some scholars are of the view that the time for the afternoon or evening adhkar extends until ‘Isha.

Al-Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said:

The author (may Allah have mercy on him) said: Chapter on dhikr in the morning and the evening.

What he meant by morning and evening was at the beginning of the day, and at the end of the day and the beginning of the night. The morning begins when dawn breaks and ends when the sun has risen at the forenoon. And the evening begins with the ‘Asr prayer and ends with the ‘Isha prayer or thereabouts. End quote from Sharh Riyadh as-Saliheen

Another time at which it is mustahab (desirable) to remember Allah (dhikr) and offer supplication (du‘a) is the last hour of Friday, because of the hadeeth of Jabir ibn ‘Abdillah (may Allah be pleased with him) who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: “The day of Friday has twelve hours, in which there is no Muslim slave who asks Allah for anything but He will grant it to him, so seek it in the last hour after ‘Asr.”

[Abu Dawood and an-Nasai]

See also questions no. 82609 and 112165

We have not found anything about the virtue of the time between the Jumu‘ah and ‘Asr prayer. Based on this it may be said that there is nothing wrong with singling out this time for dhikr, so long as it is not based on a belief that there is any particular virtue in this time; rather it is because it is when one has the time or energy.

With regard to the time between Maghrib and ‘Isha’, this is the time for the evening adhkar according to some scholars, as stated above. Others said that it is mustahab to offer nafil (voluntary) acts of worship in general at this time, as was stated by Qatadah and ‘Ikrimah. See: al-Bahr al-Muheet by Abu Hayyan.

And Allah knows best.