Why is my timer local script not working and can i fix this?

1:

while wait() do
    script.Parent.Text = "time left:"..script.Parent.Parent.Time.Value
end

^^^this is inefficient do something like this:

local Par =  script.Parent
local Time = Par.Parent.Time

while wait() do
   Par.Text = "time left:"..Time.Value
end

2:

To make the gui appear you have to :FireAllClients() and then .OnClientEvent() in a localscript make the gui appear for example this should be working:

game.ReplicatedStorage.RemoteEvents.RemoveCash.OnServerEvent:Connect(function()
game.ReplicatedStorage.RemoteEvents.RemoveCash:FireAllClients()
end)

The LocalScript:

local plrgui = game.Players.PlayerGui
 local time = plrgui:WaitForChild("Events"):WaitForChild("Time")

game.ReplicatedStorage.RemoteEvents.RemoveCash.OnClientEvent:Connect(function()
    plrgui:WaitForChild("Events"):WaitForChild("TextLabel").Visible = true
    for i = 1,time.Value do
        wait(1)
        time.Value -= 1
    end
    if time.Value <= 0 then
        time.Value = 300
        script.Disabled = true
    end
end)
local Par =  script.Parent
local Time = Par.Parent.Time

while wait() do
   Par.Text = "time left:"..Time.Value
end

I didn't test it but it should work.