Can I record posts for moments in the past?

No. Even Mind is designed for in-the-moment recording exclusively. You’re meant to record almost on impulse, without overthinking things. Doing this has many benefits, including giving you data that is outside of your self-narrative, and ensuring maximum accuracy.
While reflecting on the past is important, Even Mind is meant for live recording of how you feel in the moment. There is no way to record moments past, but you can record how you currently feel about a past moment by including a note about this past moment in your recording.