Ideally, you should set staffs' hourly rates for a case prior to start entering time for the case.  If no case specific hourly rates are set for a particular staff, staff's global hourly rates will be used for billing calculations in time entries.

After entering a few time entries, suppose you set a new hourly rates for a case, the old entries will not be automatically changed to reflect the new time.  This is done intentionally to handle a scenario in which your client negotiates a new rate in the middle of the case and you still like to bill the client at old rates for the work already done.

To change old time entries to reflect new rates, simply click on the "Edit" button next to a selected time entry, click inside the "Tenth Hours" box and click outside the box.  The amount in the "Total Cost" box will show an amount according to the new rate.  Save.