How long do you stay in heaven before you reincarnate back?

i believe in reincarnation and one idea of it is that we choose to be reincarnated and choose what we come back as. if that's the case, then it's up to you when, right? other reincarnation beliefs say that karma controls when and what, so it may not be in our control. plus, there's the idea that time in heaven is not consistant with earthly time. 1000 years can be a blink of an eye. there's no telling how long one might stay there before returning or if they'll even return.