Why wont is this script accurately work?

Ok so I have a game with colour changing windows that change every 240 seconds. White-Reflection 1 and New Yella-Reflection 0.

But the problem is the windows will become yellow in mid day, not 6:00 PM Its really annoying! I also have another that is 100% accurate ( For dynamic lighting) It works because i used "Get minutes after midnight"

Here is the 2 scripts i used

while(wait())do
local l = game.Lighting:GetMinutesAfterMidnight()/60 -- Get hours after midnight :3
script.Parent.Enabled = l<6 or l>18 -- If it's before 6AM, or after 6PM turn it on
BrickColor.new"(Bright Yellow)"
end

I need this "Minutes after midnight" in here V

while true do 
wait(240)
    script.Parent.BrickColor = BrickColor.new"Institutional white"
    script.Parent.Reflectance = (1)
wait(240)
    script.Parent.BrickColor = BrickColor.new"New Yeller"
    script.Parent.Reflectance = (0)
end 

Because, the minutes after midnight is so much more reliable.