I'm assuming LilyWDW is checking the same or similar sites that I've been checking (Team Portkey on Facebook and Mugglenet). The first wave of emails on both sites were going to the younger ones needing parental permission. So far the recent/current wave seem to be going by day of quill entry. No way to know for sure since there are 1,000,000 entrants from all over the world and these are just samplings. It makes sense, from a database sorting process, however. I'm sure all the parental permission entrants were in a separate database and they may well have segregated each day into another. Simple matter to just start downloading from each database.
If you use EXCEL, just visualize each day as a separate worksheet with the parental permission entrants on a separate one as well.
Now, what that means for the actual entry between mid-August through September is anyone's guess as we don't know what criteria Pottermore is going to use. Also, the chart that postulated each day corresponding to a specific week is already out of date due to the push back to mid-August. Having beta tested other programs, my guess is that they aren't using a hard and fast schedule (I've never known a beta tester to do so since a programmer can't know for sure how the system will respond to additional stress). Rather, they will add their first target group, stabilize the program, add the next batch, stabilize, etc. Consequently, the difference between first batch and second may be several days, between second and third, may be a single day, third and fourth almost a week, etc. depending on the stress to the servers once larger groups are admitted.
Anyone on here help beta test VMK or Wizard 101? If so, remember the times they put out the call to have everyone log in if possible? Those were stress tests of the servers. Some were successful, some crashed the system and required a lot more tweaking before the next test.