you have classic signs of over watering(yellowing leaves and flower drop).Â
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Being in the sun and heat all day and the withering based on that is different than a withering due to lack of water. In my experience with high daytime heat here in Texas(90+ for the last 5-6 weeks), no matter how much water you give during the day, doesnt help, and usually only hurts them(back to the over watering comment). They recover at night. If they are not recovering at night and continue to be withered, then water them.
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Benvenuto Arianna. I hope you stick around and enjoy The Hot Pepper! Yes, too much water. Good luck with your plants!  Maybe remove your last name from the profile.