I have a bowl of 'dry' mix available at all times (nuts, pellets, dried fruits, etc). We put out a fresh food mix with different veggies, lentils, quinoa, etc. We only leave this out for couple hours at most because since its fresh / wet, it will start to go bad or develop bacteria, so you pull that out of the cage or off the stand after a short time.
Birds don't usually gorge or overeat, they eat when they are hungry or want a snack, and then go about playing or napping. We always have food to throw out in the bowl. Actually I try to pile up the 'throwaway' and toss it out to the wild birds outside. Especially with the winter we are having here in PA!