As @mlivesey already mentioned: The 30 days are not due to a promise or something similar, but mainly due to technical reasons (including a similar buffer as it is the case for hyper early as well).
The production is split in two batches to avoid potential loss of Mainboards and components, and instead be able to test finished tablets for the hyper early. Once that testing is completed, the hyper early are shipped and the early immediately go into production (if no adjustments have to be done to any part of the assembly). The production of the bigger batch takes about 3 times as long as the first batch, that also has to be factored in, simply based on the quantity.
So there are multiple scenarios:
Realistic one is mentioned by Konsta, incorporating buffer to be on the safer side.
The potential absolute best scenario is that the hyper early birds get produced and shipped by July 8. The early birds would be shipped by July 28. This would mean that everything goes ideal, no buffer is needed for any reason, all shipping between plants goes the fastest possible, no error is found during any of the production steps and all devices produced are of highest quality. So please don't put your hopes on this but rather be surprised and happy if you receive your device prior to mid-August!