The current release time is beginning to take shape. The current timeline is as follows:
7 Sept - Branch-off and beginning of ZHF
11 Sept - “Beta” release
25 Sept - End of ZHF period? (Not officially set)
28 Sept - Hopeful 20.09 release? (Not officially set)
See the github issue for a more detailed description of events: 20.09 Timeline · Issue #95535 · NixOS/nixpkgs · GitHub