memorized from before.
In other words what you review is much more important than what you are about to memorize.
For example, do not try to be like Ibn Taymeeyah and memorize by reading once. You have to repeat and repeat and repeat until you actually get a mental picture of what you have memorized.
In other words you have repeated it so many times you can picture the page in front of you. When you can do that you have memorized it without doubt.
It also means…
You memorize little and review much.
Let us use an example:
You are memorizing Qur’an, and if you wish the three fundamental principles, or 40 Nawawi. So what do you do?
Do you take Surah Anfaal and try to do it in one shot? And then take 20 Hadeeth from 40 Nawawi or 20 lines from the 3 principles?
Maybe if your name is Ahmad Ibn Hanbal or Ibn Taymeeyah or Imam Ash Shafi’ee then go ahead.
Note well: Imam Ash Shafi’ee memorized Muwatta in eight days and I heard a story of Ibn Taymeeyah from a tape of Shaikh Ahmad An Najmi 
that a man came to him and
wrote ten Hadeeth for him on a board. He looked at it once and memorized it. And then he wrote another ten. The Shaikh read the Ahadeeth once and memorized it. And the man
did that until he reached 70 Hadeeth in one day.
As for Imam Ahmad Ibn Hanbal, well we do not even need to go into that. One million Ahadeeth, nuff said.
If you are not then take this advice
You memorize 3-5 lines of the Qur’an and 2 lines from the three principles or one Hadeeth (if it is short) from 40 Nawawi.
When the month has ended you have at least…
5-6 pages of Qur’an (1 Juz every 4 months) and at least 20 Hadeeth from 40 Nawawi.
So the next month (and by that time your brain may be stronger) you would have 1/2 a juz and the rest of 40 Nawawi.
And you continue…
So the calculation is that once you go upon this advice for two years you would have:
6 Juz and 240 Hadeeth (at least 190 from ‘Umdah Al Ahkaam)
In about 4 years you have…
12 Juz and 440 Hadeeth or even more. Because your memory may be stronger and your vocabulary bank may be larger. So I would assume about 15-16 Juz and 500-550 Hadeeth.
And by 8 years you memorize the Qur’an and you have a further 500 or 700 (1000-1200 Hadeeth)
See how it is when you take it step by step?
And this is by taking less than an hour to memorize. And if one takes more than one hour to review then this is a must.
As for another two hours it is needed to…
Review what you have memorized during the day itself, by reading it twenty times (1/2 hour or less). This could be done at the same time as the review in the morning.
Review the Mutoon that have been previously studied.
And this can be done before and after the Salaat, during Lunch or otherwise.
So if you studied the three principles then you take time to read through some of the explanations of the book.
And then another two hours are needed to…
1. Read books/ Do research/ give Da’wah (if one is capable of doing so)
2. Study new Mutoon (treatises) whether this be in the masjid (preferable) or listening to the tapes of the scholars. And this is whether the person is memorizing or not memorizing
the texts because not everything studied is memorized. Rather for every science one should memorize one text that covers the whole science.
And this should be done either after Isha or the last third of the night. However, everyone needs to arrange their time according to their capacity. But these six hours are precious every day
and if lost then we ask Allah’s help and safety.
Therefore, my dear brothers and sisters do not waste your time and use it to the best of your ability. And if you decide on which six hours to use do not let ANYONE distract you
from that.
Wa Billahi Tawfeeq.
Miftaahul-Ilm - Key to Knowledge 