You should start to be able to see the fruit right at petal fall. as the fruit gets bigger (3-5mm) the anthers get closer and closer together. If they don't tighten up the apple normally will not be viable, and either did not get pollinated or you may have nutritional problems. How old are they? A lot of semi dwarf trees that put out blooms there first or second year after planting do not end up putting out fruit. Nothing to be alarmed about. Dwarf feathered trees should put out apples in 1-2 years.
You may just be seeing a bust year due to an over crop last year if you did not have much of a bloom. It may not be weather related. Try and thin some in the future if you have another big crop to avoid boom and bust years. Good luck!
Its the same problem I had WTNUT over half my apple and pear trees are not producing apples this year so I am counting on a few of my 3rd leaf apples for some fruit and I have a few trees that are loaded and some others are doing ok. I have a few trees fruiting for the first time so I cant blame weather so Maya is right I didn't thin enough last year during boom year