1) I think the timing is too tight.
2) You would probably make the boat dock or monorail by 7:45, or so.
. . . the boat will be about 20-minutes, if you catch the boat right away
. . . the monorail is about the same, since goes clockwise
3) Once you get to Ohana, the window seats will be gone.
4) It is very possible you can't see fireworks from the table you get.
5) I would change the ADR or change the date.