Youre never gonna get the requests sent at exactly the same time (to the 1/1000th of a second) so how much do you need the requests to be sent/received at the same time?
Quick/easy way of doing this could be to create two test cases, each test case has 1 request in it. Then id execute the containing testsuite in parallel mode. This should execute the tests simultaneously
Ive just reread your post. Does this execution have to be at a predetermined time? If "yes" there's probably a better way of doing it, but you could create a windows task to execute testRunner at a specific time.