I answered a question on Stack Overflow and it got an upvote. After a great several minutes I went to Meta Stack Overflow, and was surprised that my reputation was still 10 less than main, indicating that it was not up to time. Dear me it's been a quarter. Then I tested on another site and it seems to have the same problem. How can that happen?
It has always been this way - the per-site metas don't update reputation on their main sites fast.
The reason is presumably the load on the server. Especially on the bigger sites like SO, synchronizing the reputation of all users must be an arduous process. But this synchronization does not affect the functionality of the site much. Only if a user crosses a reputation threshold, does it affect their ability to take actions on the per-site meta.
So, it is quite reasonable for the per-site metas to not synchronize the reputation levels too often.