Agree with the advice. I'd do/consider these things, in this order:
1. Do I want to "burn" a park day for only a few hours? It costs the same (one day's admission) if you show up at 8am or 5pm.
2. Assuming you do, is MK the right park? For April 27, it seems MK is open until 10pm. But there are no Extra Magic Hours that night, and MK is open the latest of the parks. That means you'll probably have the largest evening (park hopper) crowds.
3. Assuming MK is the right park (and I think it is, especially for a first trip), I'd head to Adventureland first, but take my time. Soak in main street, the sights, sounds, smells. Gasp as you come out from under the train station onto main street the first time - it is always breathtaking, but there's only one first time.
4. I'd work adventureland as others have said. FP the jungle cruise, ride Pirates, see the tiki room. Be sure to watch "wishes" the fireworks show. After the fireworks, Tomorrowland might empty out a bit - but you'll be back to MK on another day.
5. If you don't get to Tomorrowland, make it your first stop, EARLY, on the next day you come to MK.
6. Stay until 10pm - the last hour or so should see diminished crowds, and the park is beautiful at night. You're paying for the whole day, so might as well stick it out.
Give strong consideration to #1. You might be tired from the travel and can just check out the hotel pool that afternoon, saving a bit of $$. Also, mornings are when you'll get the most out of a park - And you'll want to be well rested for the next day. I'd consider an early bedtime and then go to either Epcot for early magic hour 8am, or to Animal Kingdom at 9am, with plans to stay through the evening Extra magic hours. Either way, those are long days that start early and have LOTS of walking!
have fun!