Okay, I just sat out on the porch to maybe see or hear something out of the ordinary too. Sure enough, I heard some really weird pop and a burst of light come from my mailbox. I went back and checked and the letter was gone. I wasn't prepared for anything, but I subtracted the time it took to go to my mailbox and check on the letter out from when I actually stopped the timer. It looks like it took about nine minutes and fifteen seconds.
I may do this a couple more times to get an average time, but yeah, at least it doesn't take long.
Neat. It's still a bit early yet, but if you respond quickly enough, I may be able to read and write one more letter before the library opens.