This is all just a theory so please don't grill me if you don't agree. Just ignore me if you don't agree. If anything, I'm just trying to make sense of the shipping times. This applies to U.S. orders only for the 42 mm space grey sport. This is based on historical tracking of when people got their confirmation and when people's credit cars have been charged for the last two days. It shows that Apple is completing 10 second increments (based on your confirmation receipt time) worth of orders each day. If you were in the six minute range and you already got charged, or if you were in the 1 minute range and you haven't been charged, then it's likely your mail server time was off.
Here's my guess of when orders will be processed.
Confirmation received
xx:03:50 to xx:04:00 Will prepare for shipping on 25-Apr
xx:04:00 to xx:04:10 Will prepare for shipping on 26-Apr
xx:04:10 to xx:04:20 Will prepare for shipping on 27-Apr
xx:04:20 to xx:04:30 Will prepare for shipping on 28-Apr
xx:04:30 to xx:04:40 Will prepare for shipping on 29-Apr
xx:04:40 to xx:04:50 Will prepare for shipping on 30-Apr
The 10 second increment fulfillment rate might not apply past this point.
xx:04:50 to xx:05:00 Will prepare for shipping on 1-May
xx:05:00 to xx:05:10 Will prepare for shipping on 2-May
xx:05:10 to xx:05:20 Will prepare for shipping on 3-May
xx:05:20 to xx:05:30 Will prepare for shipping on 4-May
xx:05:30 to xx:05:40 Will prepare for shipping on 5-May
xx:05:40 to xx:05:50 Will prepare for shipping on 6-May
xx:05:50 to xx:06:00 Will prepare for shipping on 7-May
"xx:04:40 to xx:04:50" is what I believe to be the window of time where orders went from a "4/24 - 5/8" delivery to a mid-May delivery. My guess is that the rate of online pre-orders waned off around this time and so the 10 second increment per day estimate no longer applies past this point. Folks in this confirmation time range and after came in at the tail end of pre-order craze so by 1-May Apple might be processing at a faster rate than 10 second increments per day. Maybe something more like 30-40 second increments per day.