Day and night cycle

Dawn lands at 4:30 AM and dusk at 7:30 PM. One in-game minute takes one real second, so an in-game hour costs you a minute: 15 real minutes of daylight, 9 of darkness, 24 for the full cycle. Every new world opens at 8:15 AM, comfortably after sunrise, which gives you most of a day to put up walls before anything comes looking for you.

One convention to keep straight: the sun comes up on the left side of the map, and the game calls that side west. Anything that announces a direction, an approaching invasion for instance, uses the same convention, so an army arriving from the west is arriving from the side the sun rose on.

Nothing displays the clock by default. The cheapest fix is a Grandfather Clock, which shows the hour to anyone within roughly 80 tiles across and 50 up or down, and gives the exact time if you interact with it directly. For something you carry, the watches ladder up in precision: copper and tin round to the hour, silver and tungsten to the half hour, gold and platinum give you the minute. Anything with a gold or platinum watch in its crafting tree keeps that readout, which covers the GPS, the PDA, the Cell Phone and the Shellphone. Time Hair Dye is the joke option, coloring your hair by the hour, and it is genuinely enough to tell noon from late afternoon at a glance.

• The Enchanted Sundial jumps straight to the next dawn and the Enchanted Moondial to the next dusk. Each carries a seven day cooldown, so they are for skipping a wait you care about, not for routine travel.
• Sleeping in a Bed runs the clock at five times normal speed, putting a full day and night under five real minutes. In multiplayer every player has to be in bed, and nobody can sleep while a boss is alive or an event is running.
• Journey Mode adds a straight time multiplier from 1x to 24x, plus presets for dawn, noon, dusk and midnight. It stacks with a bed, which compresses a whole day into about 12 real seconds. The sundial overrides both and simply moves the clock.

Night is a different spawn table on the surface rather than a darker version of the same one. Demon Eyes and Zombies replace the daytime critters, Wraiths and Possessed Armor arrive once you are in Hardmode, a Werewolf appears on full moons, and the Snow biome adds Wolves and Ice Elementals. Nearly all of it runs or flies away at dawn rather than fighting to the death, so a night you survive costs you no loot, only time.

Bosses follow the same clock. The Eye of Cthulhu, Skeletron and all three mechanical bosses can only be summoned after dark, and they flee or become effectively unkillable at 4:30 AM. Summoning at 7:30 PM gives you the whole nine real minutes; summoning at 3 AM wastes the item. King Slime works the other way, only appearing on his own during daylight, though the Slime Crown ignores the hour.

Shops shift too. The Arms Dealer only stocks Illegal Gun Parts after dark, and several other NPCs rotate a line or two with the clock. If something you remember buying is missing, check the time before assuming the world broke.

The practical version is short. Build, mine and travel in daylight, when surface spawns are thin and you are not paying for torches. Line boss summons up with dusk so the fight has the full night to run. Keep a bed at the base to burn through a night you have no use for, and hold the sundial for waits that actually matter, like an NPC cooldown or a crop cycle. If you are chasing something that only happens at one end of the cycle, sleeping through the other end is faster than waiting and much faster than standing around watching the sky.