I think this goes to say that you could potentially adapt to going to bed earlier than 1am (eg. if the above is the only thing that works for you to modify your sleep routine, just keep staying "up later by 4h" for 5 days straight, and you'll be going to sleep at 9pm on the 6th day). If it's related to daylight/nighttime, you can move locations to where days are shorter or the TZ is more misaligned (eg. don't go to Spain or France which are largely in the wrong TZ).
My entire point is that it's likely sociological for you: you either drink your last coffee at 7pm and this keeps you awake for another 6h, or you get into a routine at a particular time, or... As in, your original claim that you "simply can't wake up at 6am" seems unrealistic since "6am" is a thing that means different things in different locations.
My entire point is that it's likely sociological for you: you either drink your last coffee at 7pm and this keeps you awake for another 6h, or you get into a routine at a particular time, or... As in, your original claim that you "simply can't wake up at 6am" seems unrealistic since "6am" is a thing that means different things in different locations.