I would think the seeds themselves are fine with sun and heat, but once they germinate the baby seedlings could easily be fried by direct sunlight as intense as you are getting.
You might consider propping up a thin cloth over them, for their first week or two, so they will get bright light but not direct sun. I have what we call "frost cloth" that cuts the sun's intensity by about 20% and it is perfect for seedlings out in the sun.
