My input as a digital marketer is that the half-life of an email is generally extremely short, like an hour or less. That means that the vast majority of people who open your email will do so within an hour of your sending it, and the returns diminish greatly the longer it's "out" there. For that reason, I always advise clients during email campaigns to time the send for an optimum time for the best open rate.
For B2B, that's often about 9 a.m., because people check email when they first get into work, or around 1 or 2 p.m. because they also always check after lunch. For B2C, some people check personal accounts during the day and some not. Our biggest uptick on B2C is at 9 p.m., presumably when the kids are in bed and mom and dad are settling in front of the TV/smartphone.
All of this is to say, in theory it doesn't matter if you send it out at 2 a.m., but you should really monitor your open rates by the hour and experiment to see what works best for your list.
Another trick I do depending on the list/email is to resend the email up to 2x to the people who didn't open it the first or second time with a new subject line. That way your lovely crafted email gets the most mileage, and it's simple to do with most email service providers like Mailchimp and Getresponse. This is obviously tougher if you're emailing people from your personal account, although you can install a free/inexpensive service like Yesware to help track that stuff from your Gmail.
Last comment: I personally read all my email unless I've been gone all day/week and am overwhelmed, so all my above comments don't apply to me, and they may not apply to you. But they very likely apply to your list, because the majority of people behave exactly as I described above.
