I struggled with this for a while until i found you need to apply graffiti and fx as a filter.
I put a text clip on the timeline, delete “sample text”, open the filters from the text clip, select graffiti or fx,
Click on the graffiti or Borisfx logo, The boris interface comes up, select the effect you want, change the duration to what you want, hit apply, now in the vegas timeline and you can preview.
If you try to do the above, but as an fx rather than a filter you wont be able to adjust duration.( I wasted a week on this)
I hope this helps.
Jay Allen