Update As of 4.0.4 use of the Data Mart is not recommended, instead you should be using the added RIODS tables, this is the relevant excerpt from the 4.0.4 New and Noteworthy page.
ETL for Timesheet Entry Data The Timesheet Entry Data ETL is now loaded into the data warehouse. The advanced server property named Ignore Timesheet Data enables and disables this data collection job. The ETL is disabled by default. The Timesheet Entry Data ETL is stored in the following data warehouse table: RIODS.TIMESHEET. The following tables are also populated during the ETL data collection job: RIODS.TASK, RIODS.TASK_DETAIL, RIODS.ACTIVITY, RIODS.TIMECODE, RIODS.TIMESHEET_TIMECODE_LOOKUP, RIODS.REQUEST_ACTIVITY_LOOKUP and RIODS.TASK_REQUEST_LOOKUP
Lots of questions about how to pull your time back out once you go ahead and add all your time tracking data into RTC. Working on tracking down more details but at first glance it looks like this is fairly straight forward. Unfortunately at GA this was not included in the ETLs for CLM DW so you need to use BIRT.
Try the LIVE_SNAPSHOT create a data set using the Jazz Simple Data Set and select the table com.ibm.team.workitems.TimeSheetEntry. Not the most comprehensive bit of advice but if you take a look at that columns of the table you will see that this gives all you need to query by project, code, user, and date so should be good for reporting on where you time is being spent if you are using time tracking today. To associate this with the corresponding workitems you use the LINKS table in the COMMON_SNAPSHOT to relate the workitem to the timesheet entry.