then, yes, they will be the same length as long as you record the whole speech. If they aren't the same length, the speaker's mouth will get out of synch with the audio, and it will be obvious.

If you need to fix something like that, there are a lot of appoaches like splitting the audio at some point and moving it back into synch.

Also, a good audio editor can speed up or slow down an audio clip so that it will last a precise amount of time. They do this in such a way that you cannot tell that the speed has been changed. Of course, if you make it 5 times faster, the change will be obvious.