You can easily farm scarp metal at a night endlessly without worrying you will be running out of time because with this guide the time will be frozen in that night: You must explore only in Corn Fields or Snow World at a night, do not kill any zombies in other areas and do not kill zombies behind you and zombies in the edges of all areas just pass them and run straight, when you reach the edges of this two areas go to next area and come back. keep doing this to farm scrap metal without any limits in Corn Fields or Snow World.
important tips: only kill zombies if you have to, those who are standing in your way, other than that the night will be over.
Farming in Night 2 is the best in my opinion because zombies are easy to kill with AK-47, while crouching you can 2 shot them in the head, with this strategy you never run out of bullets and you get even more ammo by destroying chests.