Many owners free-feed their birds. Some top up the food dish as needed while some feed a certain amount and will toss food out after a certain period. Other owners may feed two meals a day as a training diet or as a means to emulate how they might eat in the wild.
Whatever method you use, you should have a gram scale (kitchen or postal scale, $20-$35 at places like Walmart or Target) on hand to occasionally/frequently weigh your bird to make sure that he, or she, is at an ideal weight. Occasionally checking the keel bone (aka "breast bone") for meat is another good idea.
Best time to weigh a bird is after the "morning bomb" but before they eat.
As for myself, I only feed enough food to last one day, so they get fresh food every day. Moist foods like fruits, vegetables, grains, legumes and the occasional eggs are not left in the cage for more than a few hours.