Source code:
local Lighting = game:GetService("Lighting")
local TweenService = game:GetService("TweenService")
local DayLength = 1 --In minutes
local DayLengthInSec = DayLength * 60
local WaitPerValue = DayLengthInSec / 20
while wait(WaitPerValue) do
local Next_Value = Lighting.ClockTime + 1
print(Next_Value)
TweenService:Create(Lighting, TweenInfo.new(WaitPerValue, Enum.EasingStyle.Linear), {ClockTime=Next_Value}):Play()
end