Regarding the speed of conforming, it’s very fast because Cinema Tools is merely altering the clip’s metadata so that the clip will play back at the new frame rate. There’s no re-encoding or heavy processing involved.
Be warned, however: Cinema Tools permanently and irreversibly changes the clip when conforming, so only conform a copy of the original clip in case you need to revert to the original.
If you use Cinema Tools to conform 24p to 29.97, it is merely changing the clip’s metadata so that the clip will play back at a faster frame rate. This will effectively speed up the clip and shorten its duration.
If you don’t want to do this, then use the Compressor method.
Regarding using Compressor to change 24p to 29.97 (30p), I neglected to mention an important step:
In the Encoder pane of the Inspector window, click on the Video Settings button. Make sure Frame Rate is set to 29.97. In the Frame Controls pane, leave Duration set to 100%. This should give you the result you’re looking for – a 30p clip that is the same duration as the original 24p source clip.