Thanks for the comments and help everyone.
I’ve redone the itinerary, concentrating more on Guatemala, and cutting out El Salvador.
2: Land in Guatemala City at 8pm. Get taxi (or shuttle bus) to Antigua
3: Good Friday. Check out Antigua
4: Antigua
5: Easter Sunday. Get a bus/shuttle to Lake Atitlan
6: Lake Atitlan
7: Lake Atitlan
8: Bus to Quetzaltenango (Xela)
9: Quetzaltenango
10: Afternoon bus back to Guatemala City. Spend the night
11: Early morning bus to Copan (arr 10am). Visit the Copan site.
12: Take last bus to Tegucigalpa @ 2pm. Spend night in Tegucigalpa
13: Morning bus from Tegucigalpa to Granada via Managua
14: Granada
15: Taxi to Managua Airport (flight departs 11am, or possibly the Paxeos shuttle)
Does this seem like a more logical itinerary?