local player = game.Players.LocalPlayer
while true do
wait(20)
player.leaderstats.Points.Value=player.leaderstats.Points.Value+20
end
output: 15:41:49.796 - ServerScriptService.overtime:5: attempt to index local 'player' (a nil value) 15:41:49.797 - Stack Begin 15:41:49.797 - Script 'ServerScriptService.overtime', Line 5 15:41:49.797 - Stack End

2 comments
Is your script a LocalScript? Only LocalScripts can use LocalPlayer.
Changed it to local script and now nothing happens, the script doesn't error, but it doesn't work either.