I’ve had them come in all seven days of the week, and anywhere from 6am ET (on a Sunday) to mid-afternoon during the week.
I’d say they’re automatically sent as soon as the examiner approves them…not send out in any kind of batch for the day. For example, when I had three approved at the same time by the same person ~6 weeks ago, they came within minutes of each other, but not all at the exact same moment.