Bus schedule to Melaque: 8:30; 10:30; 1:30; 3:30; 5:30
Bus schedule to La Manzanilla: 7:45; 9:45; 12:45; 3:00; 4:45
You can catch the bus anywhere along Maria Asuncion by just wave the bus down.
I'm sorry to say that the bus "route" to the Manzanillo airport is pretty rough - you can bus to Cihuatlan and then you'll need to take a taxi the rest of the way. Several people post here on the message board the day and time they need to get to the airport asking if anyone would want to share the cab fare.
Hope this helps