Gulangyu is small enough to cover in one well-paced day if you get the order right. This is a loop that works with the ferry schedule, the weather, and the tour-group rhythm.
08:30 — first ferry from Dongdu
Book one day ahead via "Xiamen Ferry+". Arrive 30 minutes early. On the boat, sit starboard for the Xiamen skyline view.
09:00 — Sunlight Rock first
Go directly to Sunlight Rock before the groups arrive. You'll be down by 10:30.
11:00 — Shuzhuang Garden and Piano Museum
15 minutes' walk from Sunlight Rock. Allow 90 minutes — the garden is better than the museum, honestly.
12:30 — lunch on Longtou Road
Longtou Road is the main commercial street. Stall-hop or sit down at a Minnan shop — sea shrimp noodles, oyster omelet, satay noodles. Budget 80 CNY.
14:30 — consulates walk
Walk Fujian Road and the old consulate lanes at the northwest of the island. Three churches (Trinity, Catholic, Gospel), a handful of photogenic villas, quieter than the core.
16:30 — beach and cold drink
Gangzai Hou Beach on the west or the smaller Haoyue Garden inlet. Cool off, take water shots.
18:00 — return ferry
Catch the last afternoon ferry back to Xiamen Island. Dinner on Xiamen side (save your Gulangyu money for the villas, not the seafood prices).