That's amazing how hard some authors work on promoting their own papers.
Here is a number of submissions to the astro-ph section of the arXive, by time of day, in 10 minute bins:
I took it from the recent investigation by Haque and Ginsparg.
The thing is that 16:00 (US eastern time) is the deadline for the daily submission to the arxive. So, the papers submitted at 16:01 will be the first for the next day and will appear on the top of the daily mailing. You are probably wondering why is that important? Recent research by Dietrich and also the preprint I cited above show that articles appearing the first are more visible and far better cited than others.
No matter how good your work is, just put it on the top of the list.