Not very hard, so long as you pick the right responses I don't think there's ever a time that he won't immediately rank up the next time you see him, not to mention you have a LOT of time to do so.
The only heads up is that Ranks 7 and 8 are locked off until the November Palace, and, spoilers:
If you want his Third Awakening and the extra scene after the True Ending, you'll have to pick some specific options during Rank 7, 8, and the night that Rank 10 is achieved. Luckily, these options are pretty obvious with the direction the Confidant is going, so I wouldn't worry too much.