At the end of the day 50 zombies attack. +5 per every gunshot (up to +20). When the narration reaches inside the house billy becomes a zombie if wasn't killed (the worst case scenario is 71 zombie). All achievements require you to survive the night so

Sources of zombie kills/progress in order:

• powering up activating the generator = 5 zombies if the gate was fixed
• fixing the gate = 15 zombies
• pointy sticks/hole = 15 zombies/20 if combined
• *shootin Jeremy or/and Bernard after completing pointy sticks OR hole = 20/30 zombies
• bricking up the window = 10 zombies if the door was closed/locked
• closing/locking the door = 5/10 zombies if the window was bricked up
• killing Bill/night outside the base = 1 zombie
• hiding in the open/closed cellar = 2/5 zombies
• having a bullet and a gun (not necessarily to put them into the gun) = 1-4 zombies
• *having Jeremy or/and Bernard = 10/20 zombies
• having an axe = 1 zombie

*mutually exclusive, human traps also prevent you from combining pointy sticks and hole

To prepare you have 8:00 (8 hours). Time is only spent to perform certain actions. Some actions can be sped up with the help of Jeremy, Father Bernard and Bill if you "befriend" them with glasses, a photo and painkillers. Bill can't help you outside of the base and saves less times than others.

Time consuming actions:

Moving to a close location on the map = 0:10/0:02 (car)

Moving to the farthest location on the map (not from the center/base) = 0:20/0:04 (car)

Making pointy sticks item = 2:00 -0:45 (J) -0:45 (F) = 0:30

Installing sticks trap = 2:00 -0:30 (J) -0:30 (F) -0:15 (B) = 0:45

Digging the hole = 4:00 -1:00 (J) -1:00 (F) -0:30 (B) = 1:30

Fixing the gate = 3:30 -0:45 (J) -0:45 (F) -0:15 (B) = 1:45

Mixing mortar = 0:40 (axe) / 0:10 (shovel)

Bricking up the wall = 2:50 -1:00 (J) -1:00 (F) -0:15 (B) = 0:35

Misc

It is enough to use 1 survivor as bait for the Governor achievement.

You can shoot survivors in the "overworld". Father Bernard can be shot repeatedly and resurrected and recruited by using a photo. If you shoot an "overworld" survivor his "item" icon wont disappear until you quit and reload and for all intents and purposes he's dead. Except you can shoot the icon to make a Governor trap.

Shooting the "overworld" survivor makes other recruited "item" survivor run away. Shooting an "item" survivor anywhere causes "overworld" survivors to disappear without a prompt to shoot them.

If the gun has only 1 bullet in it you wont be able to shoot the second recruted survivor who will run away unharmed if you choose to shoot him too.

You can shoot the hatch padlock but 5 extra zombies completely cancel out its effect.