I've had issues with the charge complete by field in the app (I started a thread on that about a month ago). Mine would show the time it would start charging, not the time it would complete. It is intermittent and still happens. The actual charge complete time always seems to be when it should be though, so just a problem with the car (it says the same wrong complete time in the car too) and app.
Curious, does your car show the correct charge by time?