I don`t know how many days in the game , i have never worried about it , I just use it to help me judge when things will respawn , plants will grow , ect
The game gets harder as you improve and move on in the game , so you kill mutant deer and then go to black forest you kill mutant there and search the swamp kill the mutant there .
But at some points the forest raises up against you and you get attacked where ever you are so if your in a base it may get beat up if your out in the woods you can either fight or move away from that area .
If you get a friend or friends that the game will compensate and get harder with more and more higher level monsters depending on how many friends join you . You could turn this to your advantage and harvest the loot they drop like troll skins and other bits .
A lot of the time there may be just 1 or 2 monsters here or there so it won t be to bad . Night time may get bit worse but you could sleep the night away in your hut in bed .