How to fall asleep (at an unusual time)?

Context: I’m trying to change my 8-straight-hours-at-night sleeping pattern to a 20-minute-siesta and 6-hours-at-night sleeping pattern, as part of a polyphasic sleep experiment project for potential time saving and curiosity.
In other words, my sleeping issues are completely self-inflicted and deliberate.

However, falling asleep at daytime is hard. Any tips on how to make it easier?

Tricks I’m aware of and using:
– Make a habit of it
– Use the curtains, darkening the room
– Alcohol
– Warm milk
– Follow usual before-bed procedures (brushing teeth, putting on pyjamas, etc)
– Relax muscles, use meditation to shut down motor functions
– Relaxing music (this might actually have an adverse effect)
– Use waking hours on tiring things