It really depends - I've had direct reports that have had plenty to cover on a weekly basis, and others that don't really have anything new -- the point of the weekly 1:1's is that they have dedicated time whatever they want or need from me - and it's their time to use as they see fit. If they want to skip that week because there's nothing new on their side, that's fine (but not every week), and if they are done in 10 minutes that's fine too. Other people have wanted closer to 2 hours a week of 1:1 time. It really comes down to the individual.