I'll Pseudo-code it for you....
(so don't direct copy / paste - it wont work)
SINGLTON/AUTLOAD SCRIPT
extends Node
var gameyear = -10000
var gamemonth = 1
var gameday = 1
var gameminute = 1
var gamesecond = 1
MAIN GAME SCENE
$Timer1 (enabled, internval say... 1 second to start, adjust as needed)
Connect the timer to it's method...
func onTimer1_timeout():
advance the second(s)
Singleton.gamesecond += 1
if Singleton.gamesecond >= 60:
Singleton.gamesecond = 0
Singleton.gameminute += 1
if Singleton.gameminute >= 60:
Singleton.gameminute = 0
Singleton.gamehour += 1
if Singleton.gamehour >= 24:
Singleton.gamehour = 0 #or 1? Depends how you want to id your hours)
Singleton.gameday += 1
if Singleton.gameday >= 30: #30 days in your game's month?
Singleton.gameday += 1
Singleton.gamemonth += 1
etc. etc. etc.
Let me know if you need more help.