world/New()  //  Called when world starts up
  LoadWorldVariables()  //  Calls a custom procedure to load saved global-related variables (such as day and year you would want to save)
  spawn() TimeDaySystem()  // To tell you the truth, I dunno if spawn() should be here >_> I usually spawn() off loops at the beginning <_<

world/Del()  // When the game is shut down
   SaveWorldVariables() // Would be a good idea to save the day and year that passed by.
   ..()  //  Without the parent procedure, the default action would not pass - which is needed to actually shutdown the server.\
You don't need ..() if there's no default action (usually mentioned in the DM Ref) or if you did not overwrite it elsewhere.

var  // A few "global" variables
   day = 1
   year = 0
   daytime = 1 // Boolean variable :) 1 = day, 0 = night in this example
proc/TimeDaySystem()
   while(1)  //  Infinite Loop 
       sleep(20*600)  // Define the time you want to pass before the day can change
       daytime = !daytime  //  "Inverts" value. If it was 1 (day), it is now 0 (night) and vice-versa 
       if(daytime) // If the variable is true - read the link at the bottom - means it's daytime now... which means it's the next day!
          if(++day >= 366)  //  day++ is like (day+=1) at once :) So if the added day is = or more than 366, a new year begins
              day = 1  // It's a brand new day :)
              ++year  //  Increases year. Pre-increasement variables (++var) first returns the current value of var THEN adds 1 to the var.  Post-increasement variables (var++) adds 1 to the var then returns the variable.
// For example: XX = 25
//Pre-increasement (++var)
// world << ++XX  <-- 25 [announced to the world]
// world << XX    <-- 26
          
//Post-increasement (var++)
// world << XX++  <-- 26
// world << XX    <-- 26

mob/Login() // Called when a client connects to a mob
  ..()  // Calls the default action, such as placement in the world
  TimeLoggedIn = world.time  //  world.time is the # of ticks the world was up for. You'll see why this is used soon.
  spawn() AgeSystem()

mob/Logout()  //  Called when client leaves
  TotalTimeLogged += world.time - TimeLoggedIn  //  Adds any remaining time before deletion of the mob.
  del src

mob/proc/AgeSystem()  // Know when to use usr! This is not the place. Read the link at the bottom.

     var/TimeWait = TotalTimeLogged%(60*600)  // 60*600 = 1 hour in 1/10 seconds (approx. 1 tick). % is NOT divide, it is modulus. Basically, the amount remaining...
// For example: 5%5 = 0 --> 5-5 = 0
// 10%2 = 0 --> 10-2 --> 8 - 2 --> ... --> 2-2 = 0
// 5%2 = 1 --> 5-2 --> 3-2 = 1 (it can not go negative)

// So, this will wait until the person has been logged in for 1 hour, to increase the age.

// Reason why this is OUTSIDE the loop is because we want TimeWait to be defined using TotalTimeLogged just once, since after that it'll be done exactly one hour.
  while(1)  // This lasts as long as the mob exists... when called.

     if(!TimeWait)  //  If the modulus found the result is 0, meaning it has been exactly 1 hour
         TimeWait = 60*600 // Time to wait another hour
         age++  //  Increase the age
  
     sleep(TimeWait)  // Waits for an hour, or however long it needs to be from the beginning to reach one hour play time.
    // Here, the proc will loop back to under the while() after the necessary time passes by

proc
    SaveWorldVariables()  // The proc that saves your character.
        var/savefile/F = new("world.sav") // define the save file and create it
        F["World"] << world // Outputs ALL of the character (var's, etc) into the list