Anything that’s self-imposed has been decided by you, not enforced by someone else. If you set a self-imposed bedtime of 11:00, it’s completely voluntary.
Your school’s starting time is decided by the school itself, but if you make sure to get there a half hour before your first class, that’s self-imposed. And if your mom instructs you to apologize to a friend whose feelings you hurt, that’s not self-imposed, because she’s telling you to do it. When someone is described as being in “self-imposed exile,” that means they’ve left the country of their own free will, rather than being made to leave.
voluntarily assumed or endured“self-imposed exile”
of your own free will or design; done by choice; not forced or compelled