As a batter you can ask for timeout as many times as you want.
The key to this is how often the ump grants you the time.
Putting your hand up, without any verbal communications doesnot constitute a timeout. Even if you call "Time" unless the Umpire grants you time there is not a timeout.
A good umpire which manages the game will not permit a batter to make a travesty of the game by granting unlimited timeouts.