Does anyone have an approximate idea (either based on own observation or literature) of how long apple flowers stay opened during the day in the flowering period? I can imagine it varies quite a lot between varieties and geographical regions. I am mostly interested in temperate regions at a latitude between 40°F-50°F (5°C-10°C).
So far as I'm aware, apple blossom flowers don't have periods when they close, they're not on the tree long enough. Average time for a flower to open, be functional and wither is around 7 days, depending on the weather and the speed of pollination/fertlilisation. Time lapse photography showing apple flowers over 7 days can be seen in this YouTube video: Apple blossom time lapse. Warner's King.