We had an 8:05a last summer. There is a special line at DHS for pre-park opening character dining. You can see in the pic below that there is a sign directing people to go through there to check in.
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If it's anything like when we went, you might even try going closer to 8 since it doesn't get a huge crowd and the sooner you dine...the more likely you are to make it out before the park opens. We got out w/about 7 min to spare.