Count Employees Timesheet

Hi 
I'm trying to count number of employees working in every half an hour.

1.Labor Timesheet table showing Employee ID/Start Time/End Time

2. Time table showing
Time / Half 
00:00:01 / 00:00:00
...
00:30:01/00:30:00

I d like to create a table showing how many employees working in each half an hour.

What should be the DAX and relationship between two tables?

Thank you