No, letters of support are due before the application deadline (see the program page for the exact date). As soon as you fill in the contact information for your letter writers, the system will send a message to them containing complete instructions on how to submit a letter on your behalf. You may want to fill in this section before completing the rest of the application in order to give your letter writers ample time to compose and submit their letters.

For purposes of this program, mid-career is defined as between seven and twenty years out from the Ph.D. In all likelihood, if you are at the lower end of that range, you have recently been granted tenure.