Enable/Disable Title In/Out effects for Lower Thirds

This all depends on how the title was created.

Most are done in Motion.

If so, you should be able to control-click and choose Open in Motion.

The timing of the duration of a build-in or build-out animation is often determined by special Markers in the Motion project.

These are Build-In (Mandatory) or Build-In (Optional) (and similarly for Build-Out).

If there is a Build-In (Mandatory) marker at, say, 2 seconds in, this makes the duration of the build-in fixed at 2 seconds, regardless of how much the title duration is in your project.

The (Optional) variants work the same way, except that you get a checkbox in FCP and can deactivate the respective animation completely.

Here is a scheme of the Motion timeline with these Markers:

The problem you may be experiencing is probably to setting the total duration less than the sum of the build-in and build-out times...

Control-click on the marker, choose Edit Marker and change from Mandatory to Optional.