Chania (also written Hania, and Chaniá in Greek) is the town on Crete that people photograph first. It was founded by Venice in 1252 on the site of ancient Kydonia, lost to the Ottomans after a two-month siege in 1645, and was the capital of the island until the title moved to Heraklion in 1971. All three eras are still standing in a few hundred meters of waterfront: Venetian shipyards, a mosque with no minarets left, a lighthouse the Egyptians rebuilt, and a church that has both a bell tower and a minaret.
It's a small town with a lot of tourists, and it knows it. The harbor is crowded from spring to autumn, but the lanes behind it, Splantzia and Topanas, are still lived in, and the beaches that made western Crete famous (Balos, Elafonisi, Falasarna) are day trips of one to two hours. That is why five days works: two on foot in town, then three that leave it.
This plan is written for the shoulder season and for November in particular, because that's when many readers ask. Sea and air are both around 19-20°C, but beach bars and boats are closing, the Samaria Gorge is shut and the restored market hall isn't open yet, so the plan says what to do instead. Day one is the harbor, day two the old town lanes and the museums, day three the northwest (Balos and Falasarna), day four Elafonisi and day five a half day in Rethymno. Start on a Wednesday: the Maritime Museum is closed on Sundays, the Archaeological Museum on Tuesdays and Etz Hayyim on weekends, and a Wednesday start keeps all three open on the days they're used. Greece is the country context, and if you want the other end of the island, the plan for Heraklion picks up where this one stops.