Just keep in mind it may not work out, and go with the flow. The last time we ate at the Wave (a few months ago), we walked in at 7:15 to check in. They were running late (and told us at that time). We weren't seated until 7:40, it took a few minutes for our server to make it to our table. We ordered right away, got our food a little after 8, and asked for the check when our food arrived. We didn't leave the restaurant until around 8:20, at which time we had to join the line of people walking to MK - there was one temp check tent (with 2 sides), but it still took us about 10 minutes to get through it. We still got into Magic Kingdom a little before 9, but no way we would have made it for 8:30. I'm not saying that will be your experience, but you may hit a few bumps with the timing. I will say the breakfast was very tasty!
ETA: It's funny timing for this thread for me. Yesterday my husband and I were planning our next trip. My favorite place to have breakfast to make a park open by walking is Trattoria al Forno on the boardwalk to get to HS. So when I said I wanted to do a breakfast again that's what I was thinking of, but my husband immediately - without skipping a beat - said "We're are not doing the wave again." That was definitely a stressful morning for us (we like to be ahead of the pack at park open which is why we tried the wave), but I hope our experience was outside the norm and your morning getting to MK goes flawlessly!
