If can't feed a flight pond daily, can I do it weekly instead?

You can, but lots of things can go wrong. For example, piles of food can easily attract rats and even a gang of scavenging moorhens can be a nuisance. Flighting patterns can become very irregular, especially at around the time of the full moon. Ducks that have the opportunity to stay late in the morning, and keep feeding, may well be late coming in next evening. Also, if corn starts to ferment, there is a risk of water pollution.

If you cannot feed daily, it pays to consider buying an automatic feeder. This can be set up to scatter a little barley into your pond late each afternoon, just in time for the ducks, and after the moorhens have gone to roost.