No matter what schedule you will design, there are some things to consider before making choices.
The BRAC Gap Rule
If sleeps are too close together, it seems that the body cannot distinguish between different periods of sleep and will act as though the two sleeps were one disturbed sleep. This means the ultradian rhythm becomes disturbed and that period is treated as a missed core sleep. Keep sleeps apart from each other at least for the length of your BRAC. This used to be the 2h Gap Rule, but for people with a 1.5h BRAC they may better have a 1.5h Gap Rule.
3h Total Sleep Rule
It is regarded by sleep scientists that 90 minutes of SWS and 90 minutes of REM are the ideal amounts of sleep needed by a human adult. Any less than this and you begin to suffer traditional sleep deprivation. It may be that someone can reduce their sleep to less than this, but with this reduction comes many health risks that are linked to traditional sleep deprivation. These risks can include but are not limited to loss of focus (and accident), memory loss and brain dysfunction, insulin resistance (and thus diabetes and obesity), and a weakened immune system (leading to heart disease, increased cell toxin count and cancer). Uberman Sleep seems to be the best way to manage less than 3h total sleep; Uberman is not undoable long term, as there is evidence that higher frequency sleep also reduces the need for total sleep.
Mornings yield better REM than afternoons
REM sleep has a circadian rhythm with an acrophase around dawn and SWS has a circadian rhythm with an acrophase around dusk. Basically, sleep in the mornings between midnight and midday yield higher amounts of REM in healthy subjects, whilst sleep after midday and before midnight yield higher amounts of SWS.
You should aim to get a core sleep early in the night (between night fall and midnight) to maximize SWS depth and quality, and then you may aim to have REM naps in the early mornings and around midday, forgoing naps in the night.
If you nap at night time and take a core sleep around dawn, eventually your circadian rhythm will phase shift toward early mornings, causing pre-dawn SWS, and morning tiredness if you do not get adequate morning REM naps.
Long Sleeps are different to short sleeps
Unrepartitioned long sleeps (60+ minutes) allow for the body to get SWS, whilst shorter sleeps will generally aim to get LNREM and REM sleep. Athletes, for example, may benefit more from a schedule that has enough long sleep in the afternoons and pre-midnight, as GH secretion from SWS will be required for them to do their activities. Academics may benefit from trying to balance their schedule more toward frequent short sleeps in the early morning and before midday, as memory consolidation is associated more with REM.
Picking a Core Length
Searching at the internet, we found about as many variations of this graph as there were made.
Kazerniel collected data from 9 of the graphs and combined them into a meta-graph. This shows the average occurences of REM according to the various graphs.
With this, it seems like that the following times are the most likely occurences of REM for a monophasic sleeper:
1.25h – 1.75h, 3h – 3.5h, 4.5h – 5h, 6h – 6.75h
This has great application because waking up from the end of a REM stage is the easiest way to wake up. This is because the brain wave frequency most closely matches an awake state, compared to NREM which is sometimes significantly lower frequency.
These times will change as you change your sleeping patterns, or shift your circadian rhythm. This graph has the assumption that core sleep initiation starts before midnight, and the person wakes soon after dawn.
The 2-cycle core
It is fairly important for people to focus on the 2-cycle core because that is the most commonly practised (and likely easiest) core length. Segmented Sleep, Dual Core and Everyman sleeping patterns all use the 2-cycle core as the basis for their schedules.
Older people are more likely to have a 2 cycle core length closer to 3h long, and younger people are more likely to have a 2-cycle core length closer to 4h long. Teens may have a 2-cycle core length that extends greater than 4h, which both follows the age-length trend and helps accounts for the extra sleep they need.