I only drink coffee but a friend of mine dips two teabags in and out of a teapot quicker than I can write it. She fills two cups at a time saying by the time she has drunk the first one the tea in the pot will be too strong. It seems a waste of money to me, she's only drinking coloured water.
There was an article a few months back, can't remember where, by a man who had made exhaustive tests and tastings. He concluded that the optimum time was 25 seconds, stirring only once, thus making sure you are not overloaded with tannin.