Different varieties are ready at different times, so if you know the names you can look up when they should be ready. To tell if they actually are ready, lift a fruit gently in your hand and give it a small twist. When it's ready the stalk will disconnect but if it's unripe you would have to pull hard to remove it. Check each apple in the same way as they don't all ripen at exactly the same time on each tree.
Well done for getting such a good crop so soon. We live at 1000' above sea level in Scotland which is just about the altitude and latitude limit for apples. A couple of varieties are doing well but the new trees I planted last year have died of canker, probably because they were stressed by the unfavourable conditions. The bigger trees have canker but still seem able to produce fruit. I'm loathe to chop them down as then we would have none
