Each task has a timer you can start, stop. It helps you accumulate and log time you spend working on that task.

You can then obtain a timesheet report by opening the Progress & People tile. At the bottom there is a Workload link. That gives a summary per project for the entire team on the initiative.

Or, you can obtain a timesheet for a worker by clicking on his or her name. Timesheets can then be copied to the clipboard and pasted in a spreadsheet application like MS Excel.