It’s 5:45 am for some. I’ve seen newer restaurants open at 5:30. Some Enchanting extras open at midnight; others 5:30 am. You might have to go to myplans page so the system sees you have tickets and then go to the restaurant page. Have a backup plan eg an iPad with stored credit card info
2 weeks prior to your trip Disney might add extra hours to the park and then a few days later add dining for that time.