This took about 30min once I had the parts figured out. I could have sanded the wood, rounded the corners, and painted or stained everything, but that would have added an hour or two.
If I was doing it over (or when I make the next one) I would mount the motor and winder as far back as possible, maybe have a deeper platform, to allow more of a V shape from the spool of thread through a thread guide through the tensioner and then to the bobbin, as on the store bought winder.