You do not have time for another round of canditates. That is why you are forced to take him even if do not want to.
And why don't you have the time? It isn't like he actually does anything for the single planet he is with you. Nor is an apprentice an integral component of any plans you(r companions) may have. And as I recall there are no dialogue options in that conversation for the SI to state that "he's out of time." All you can express is either that you like him or that he is alright.