Timer does not countdown correctly?

i have a timer that is supposed to be synced to all clients, but the problem is that the timer is delayed. It is supposed to go down by 1 every second. but it goes down by 1 like every second and a half or sometimes 2 seconds

Server Script in Serverscriptservice script:

local RS = game:GetService("ReplicatedStorage")
databaseService = require(RS.Infos.DatabaseService)
local globalDatabase = databaseService:GetDatabase("Global")

while wait(0.9) do
    local countdown = globalDatabase:GetAsync(500)
    if countdown == true then
        if game.Workspace.TimerValue.Value == 43 then
            local sound = Instance.new("Sound", game.Workspace)
sound.SoundId = "rbxassetid://4577580056"
            sound:Play()
        end
        if game.Workspace.TimerValue.Value == 0 then
            game.Workspace.Timer.Value = false
                globalDatabase:PostAsync(500, false)
        else
                    game.Workspace.Timer.Value = true
        game.Workspace.TimerValue.Value = game.Workspace.TimerValue.Value - 1
        end
    else
        game.Workspace.Timer.Value = false
        end
end

Localscript which is inside of a textlabel:

function SecondsToClock(seconds)
  local seconds = tonumber(seconds)

  if seconds <= 0 then
    return "00:00";
  else
    local hours = string.format(".f", math.floor(seconds/3600));
    local mins = string.format(".f", math.floor(seconds/60 - (hours*60)));
    local secs = string.format(".f", math.floor(seconds - hours*3600 - mins *60));
    return mins..":"..secs
  end
end

while true do
    wait(0.1)
    if game.Workspace.Timer.Value == false then
        script.Parent.Parent.Visible = false
    else
        script.Parent.Parent.Visible = true
        script.Parent.Text = SecondsToClock(game.Workspace.TimerValue.Value)
    end
end

It may have to do with sloppy code. I use an outside db to store whether the timer has started or not, but the actual countdown is stored inside of the server