There are hundreds of varieties of the moss rose also called ice plant and this useful succulent has wide open daisy like blooms that usually close up when shady or very hot. I suspect you grew a variety bred to stay open in the past but the organic seeds you used are most likely an older or native version of the plant and close when they get  warm. Try giving them a bit of shade with an umbrella and see if they stay open. I must also say congrats for growing these plants from seed. That is not an easy thing to do so enjoy when they do bloom. Keep growing, Marianne Binetti