I assume you are talking about the Titles and Text media generator. It does not give us any control over the animation length. The only thing you can do is change the generated media length to get the animation speed you want and then shorten or lengthen the event to get the overall length you want. If you need to lengthen the event then make sure looping is off.
If this workflow does not work for you then you can always fall back on Protype titler.