Analytics tab "locks" you to the date range for which work units are available. Are you sure there are work units visible in the time tracking page that are outside the date range you can select in the analytics tab?
Also, there is a "Limit date range to dates with work units" toggle, that is checked by default (but can be unchecked).
Just adding this in case it isn't clear (I admit it's not super-obvious): You can adjust the date range by clicking on the date field in the top bar
