Since there is no official info out from Larian about the 72 hour early early access on July 31st we just have to wait and see.
Not having the 72 hour early access for chapter 1 will make things easier for them because then they don't have to add code that would prevent players from advancing to chapter 2 if they reach the end of chapter 1 within the period.
Larian is a company listening to their customers so it might be that if they feel quite a few are disappointed we didn't get the 72 early access as we had hoped for they might announce it shortly prior to the release. BG 3 is probably going gold very soon so they could easily do it if they wanted to.
It could also be that they think getting a free upgrade to the digital deluxe version is good enough compensation for buying the game in early access and thus skipped the 72 hour early early access. However, I think quite a few larian fans would have preferred the 72 hour early access for supporting the game for 3 years. Right now a player who got the game in 2020 will get the same as a person buying the game today. If the free upgrade had already ended then it would have been a different matter.