Day Two - Antigua
Central Park and Cathedral
Shopping at market
Live music/art exhibitions etc.

Day Three - Antigua
Visit various ruins
La Azotea or Filadelphia coffee farms
Recommendations for live music or cinema

Day Four - Hawaii
Morning shuttle to Monterrico/car pickup to hotel
Check-in to hotel
ARCAS Turtle Hatchery
Dinner in the village

Day Five - Hawaii/Antigua
Boat/birdwatching tour in the mangroves
Visit La Barra, fishing village
Private car to Monterrico/Shuttle to Antigua
Back in hotel, dinner

Day Six - Lake Atitlan
Shuttle to the Lake
Stay in Panajachel
Water taxi to Santiago
Shopping, Maximon

Day Seven - Lake/Airport
Shuttle back to Antigua
Breakfast/Lunch
Taxi to airport

There is an option to do Tikal, the famous Mayan ruins, but since that is a day's journey by bus/shuttle, i'd recommend a 10 day itinerary to fit it in, or fly there in lieu of Lake Atitlan.