You are using the Timed Sequence. Then there are two time-lengths you can set: the length of the event on the timeline determines how long your text will be displayed. This is independent of the length of the effect.
The length of the effect can be set in the popup window from the video media generator (Credit roll). On the left top of this window you find the place where you can fill the length of the effect. The longer the effect takes, the slower it will go. This is independent of the event length on the timeline. In this way, you can set the speed of the incoming and outgoing text.
To make sure that the text is displayed only once, you will have to adapt the event length to the effect length (i.e. the ‘speed’)
To set different speeds for incoming and outgoing text, you either have to use a trick, or use different presets for in and out or use the pro-type titler.
Theo