I have a bit of experience in both researching and practicing different sleep patterns. My recommendations are:
Minimum 2 hours REM sleep
1-2h of deep sleep
Often you can catch up on REM sleep by napping. Sustained deep sleep only occurs in longer periods of sleep such as 3h+. It is true that hormone release is optimized by long periods of unbroken sleep.
To give you an idea of how sleep works:
A cycle goes for around 1.5h
Each cycle covers all 4 stages of sleep. Stage 1 is brief and stage 2 occupies 45% to 55% of total sleep in adults. Stage 3 and 4 are dreamless sleeps, also known as ‘deep sleep’, and goes for about 20% of a cycle, and the immune system and most night-hormones are secreted in these stages.
REM sleep occupies about 20% of a cycle. REM sleep reconfigures the brain, and is what keeps you refreshed and alert, with a healthy memory.
There are 2 common deprivations: REM deprivation, and Deep Sleep deprivation. Someone suffering from REM sleep will wake up in the mornings feeling like crap in the head, and will feel brain-fog. This is the most dangerous deprivation and can lead to depression, or a declining memory.
Deep Sleep deprivation usually makes the person feel like their body is not recovering from the most basic exercise (such as walking). You may wake up stiff and out of energy.
I have heard of many different sleeping patterns working. What you guys do is called a Siesta Sleep Cycle, which is probably the most common sleep pattern in a non-American/Australian/English society.
Because all stages of sleep occur within a sleeping cycle, if you get interrupted sleep you will be cut short from getting a portion of your later stages of sleep such as Deep and REM. Fortunately you can teach your body to shorten it’s natural cycle length from 1.5h down to anything between 45min and 15min.
You can change your circadian cycle (the process that tells your brain when it is day or night), so sleeping in the day or night does not often make a difference, though without proper stimulus it is hard to change it.
The most important thing to remember is to keep a regular schedule. Even on the weekends, you should get up at the same time every day. The more variation in your sleeping timetable, the more ‘distracted’ your circadian cycle is going to get, and the worse quality sleep you will get. With a regular timetable your circadian cycle will change your sleeping cycle lengths to optimize the amount of Deep and REM sleep it gets.
If you take ages to get to sleep, spend less time in bed in one sitting, and sleep more often.
There is heaps of information out there, you just gotta read up on it, or just ask questions.