A good question.
A local answer.

A bridge pedestrian walk offers different angles, but confirm the route and any temporary access changes.

Check actual sunrise time and first ferry service for your date; a very early ferry may not be running.

Ask the hotel whether the booked room faces the relevant part of the harbour, not merely whether the hotel has views.

If staying late would make the return stressful, book a Manly night or make the scenic ferry trip earlier.

Treat the zoo as the main timed visit and decide which one of the other two areas deserves a relaxed afternoon.

List the views or commentary you expect from a paid cruise and compare them with the ferry route.

Ask the operator which route it uses; the busiest water is not necessarily visible from every cruise.

Use the current operator timetable and service alerts for the exact sailing and wharf before leaving.

Allow a little extra time around the terminal, then focus on the ferry ride and Manly day itself.

Choose a lookout or short cruise with comfortable seating if time on the water matters more than an active tour.

Check the last service, weather and whether an outdoor deck is available before setting out.

Compare the official year's viewing-area map, age rules, entry time and whether the ticket includes a seated place.