Your chronotype is your genetically determined preference for when you sleep and when you are most alert — from the early lark to the late owl. You cannot fundamentally change it, but you can tune your sleeping times, your work and your exertion to it. Roughly half of it is hereditary.
Your chronotype is largely determined by your genes — variants of the PER3 gene, for example — and is roughly half hereditary. It also shifts with age: young children and older people are earlier, teenagers and young adults later.
It is therefore not a matter of willpower or laziness. Forcing an evening person to perform early in the morning is like asking a morning person to pull an all-nighter.
Look at your natural preference on a free day without an alarm: when do you fall asleep and when do you wake rested? That window gives your chronotype away better than any questionnaire.
The gap between your natural window and the one your working week imposes is called social jetlag. The bigger that gap, the more you catch up every weekend — and the more unsettled your rhythm stays.
If you and your partner sleep on different rhythms, that is often more important than which bed you choose. Anyone lying down hours before the other is woken by every movement on the other side.
That is exactly where a build-up per half and a bed that doesn't transmit movement make a difference — and why it is one of the first questions at the intake.
Not fundamentally. With consistent wake-up times and bright morning light you can bring your rhythm forward an hour to an hour and a half, but your innate preference stays underneath it. Adjusting your diary usually pays off more than adjusting yourself.
That is the rule rather than the exception. What helps is a bed that doesn't transmit movement and is built up per half, and agreements about light and noise during the hour you aren't in step.