Virginia,
It is funny you mention this. A few notes here...
1 - There was a report of some issues on a backend server that may have caused some performance issues or lag when updating fields.
2 - Even aside from this, the update you speak of can take anywhere from about 10/20sec to a few minutes. The reason is normally the size of your environment and the Project you are working within. The more objects you have and the more 'Jobs' or 'Server Requests' you make the longer it may take as they get queued and are handled sequentially. If there is a long running job being processed, this could slow down other updates such as updating Actual Effort from timesheet.
This is not a bug but a known behavior. So long as it does not take more than a minute or two MAX, it just means that your system is currently making a lot of requests to the server. If you are seeing very long lag or no updates at all, please open a case for further investigation.
Sincerely,
Boris