Logging/cycle length

This is my first month off bc. I haven't started af yet- I know it's normal to get af late your first month off bc. I've adjusted my period with the edit button- but my question is regarding cycle length. After this first month do I go into my profile and edit my cycle length to show this first months length? Or do I wait to edit that until I have a more clear idea of my cycle length? I don't want to miss possible fertile days because my cycle length isn't accurate.