That would be plenty of time for me. I can paint several rooms in 1 day. In 3 I could have the carpets torn out, the walls torn out and everything redone. That would be by myself. Of course I work pretty quickly, have lots of experience and the biggest factor, is wanting to get it done to see what it looks like. That's my biggest motivator.
Just to paint? or to actually gut it (new sheetrock, etc)? If you are doing new sheet rock, flooring, etc, then 3 days might not be enough time for an inexperienced person to do it all. If you are just painting/redecorating, then you should have plenty of time. Have fun!