This is getting a little close for fall cauliflower if your first average frost is mid-October. Cauliflower curd/head is more frost sensitive than broccoli, and it would have been better to start them from seeds around mid-July. You may need to consider how to protect them later on with hoops and floating covers.
Does your seed packet say what the days to maturity is? Is it 75 days or so? You need to add two more weeks for fall crop because or the shortening days.
I think if I were you, I would try both direct seeding in the garden bed and starting seeds inside. The ones outside need to be closely protected from slugs and caterpillars. You would be better off putting up insect screen/Tulle covers for them -- this could be done individually or with a wire hoop supported tunnel -- this will protect them from cabbage white butterflies, cabbageworm moths, and Stinkbugs and harlequin bugs, to name a few. Edges must be completely closed with earth staples or by burying. ...now they are vulnerable to slugs... Check frequently.
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