I know I will get thumbs downs for this, but I have spent weeks on it and haven't figured it out
Any help? I am clueless at this point
3/26/2014 Update
Here's the rough script I have so far, please comment on any errors or glitches as I continue to make the script.
local DataStore = game:GetService("DataStoreService"):GetDataStore("Time")
game.Players.PlayerAdded:connect(function(player)
wait(3)
local label = player.PlayerGui.TimeLeft.Frame.TimeLeftLabel
local ready = player.PlayerGui.TimeLeft.Frame.Ready.ReadyToVisit
local key = "user_" .. player.userId --we want to give 50 points to users each time they visit
DataStore:UpdateAsync(key, function(oldValue)
local now = tick()
local later = oldValue or 300 --oldValue might be nil
local difference = math.abs(now - later)
local left = 300 - difference
if left < 0 then
left = 0
end
repeat
label.Visible = true
local now = tick()
local later = oldValue or 300 --oldValue might be nil
local difference = math.abs(now - later)
local left = 300 - difference
if left < 0 then
left = 0
end
label.Text = left
wait(0.1)
until left == 0 or ready.Value == true
label.Visible = false
ready.Value = true
end) --DataStore End
end) --player enter end

5 comments
I would think you could just save the time they joined the game and compare it with the last time they joined using tick(). The only minor issue you may face is a day in discrepancy because of the way ROBLOX handles server time. Kenetec wrote a function somewhere to handle tick() correctly so you can accurate do this.
Thanks I will look into it and get back to you
I looked into tick a little and I am just curious, I know when you use tick() in a local script it finds the computers local time, but could it be changed if you changed you computers time?
Use os.time().
Articulating is absolutely right. Before os.time() we had to use Kenetecs method, which used HttpService to synchronize. tick() returns the local time, which can be in the worst case 24 hours off. os.time() returns what you want here, the true UNIX time, which is the same on every device out there.