Hi
In that case, irrespective of how long they ACTUALLY spend doing the tasks you can assign then as 100% on the task for the given period. The you can use the resource usage report to show how long each person is assigned to the project.
OR
You can create a custom view in Project with the information you need to show. Then export the data to Excel and change the start and Finish columns just to show the dates and not the times if you still want Project to just show the ACTUAL hours spent on the project.
Hope this helps.
Tony