Here is a basic classifcation of schedules by their difficulty level, assuming a typical sleeper with 8h monophasic sleep and normal levels of SWS and REM:
Difficulty
Example schedules
TST range
Sleep time cut
Note
Easy
BiphasicX, E1-ext,
Siesta-ext, Segmented-ext
7-8
<1 hour
Recommended for beginners or those needing significant flexibility.
Moderate
E1, E2, E3-ext, Siesta, DC1, Triphasic-ext,
Segmented, DC1-ext
5-6
1-2 hours
Require a significant adaptation process, but can be quite flexible after adapting.
Hard
E3, DC2
4-5
2-3 hours
Require harsh adaptations and are not particularly flexible for most people.
Very hard
DC3, Bimaxion, Triphasic
4-5
2-3 hours
Considered harder than the "Hard" ones because they do not contain a longer core during SWS peak hours.