Hello Eileen, great that you have a garden underway and I am so pleased the books have helped you get going.
As you say the weather has changed… Plants wilting in afternoon sun is because their roots are giving leaves a rest, from either a lack of water in soil or, more likely, they can’t pump it fast enough to keep leaves turgid. So fleece may help. Perhaps cover some and not others to see the difference. Your plants should survive without it though!
I notice beetroot looking limp in these hot afternoons and that is less problem than lettuce which needs to keep growing for quality of leaf harvest, so they benefit more than anything from some watering.