I would have told them it was due the first date you are allowed to submit your secondaries. Letters are part of your secondary application and aren’t read until the secondary is submitted. When I was applying I told all my writers the date of when the primaries were due so that I was 100% sure I would have all of them in by the time secondaries came around. Sometimes writers are not the best at getting you what you need and it puts you in a tough spot cause you don't wanna be pushy, but you want to make sure you get what you need.I've been trying to reach a professor of mine since earlier this year after he agreed to do my letter. I gave him a deadline of August 1st. However, he replied saying he would like the absolute deadline for the letter of rec. Which date would be the hard deadline? And also, do the letters have to be when sending secondaries?