Well, when you run the script, the sound position will be at 0. And you are only checking the time position when the script is ran. You would have to check it every time it updates. Also, the position would rarely be ever just a single integer, It would usually have decimal points since the sound is playing every millisecond.
My solution:
while wait() do
local timePos = workspace.Disco.TimePosition
if timePos >= 10 and timePos <= 12 then--check if its in range
print("START")
break-- end the loop to prevent unwanted stress on server
end
end
Basically what that does is loop check the position and see if its between 10-12.