As fellow readers already pointed you to and gave you some answers.. my duty is to raise concerns.

If everyone is going to a place, then the place is nothing special anymore. If everyone wear the same, the wore isn't special anymore. Everyone has the same aim as you. The aim is the same like "when to send the newsletter out, so it has the best reading reach?"

But, if everyone, who want his newsletter to be read, follow some guru tips, they land all in the same inbox at the same time.

So.. what's more important is to have a good catchy subject and actually offer something.

The posting time is irrelevant then.

May be you think twice on marketing. It's good work invested.

Peace.