According to Rockstar’s LinkedIn page , all 307 jobs were posted in July. They can also be found on the studio’s website.
The studio recruits developers of different levels and specialties in several divisions. For example, Rockstar is looking for a programmer to work on advanced physics and vehicle collision systems, as well as people with experience working on open worlds with realistic character animation.

Usually studios open so many vacancies at once when they move to the full-fledged production stage – often during it the number of people working on the project at the same time reaches a maximum.
In early July, Rockstar announced that it would no longer release major updates to Red Dead Online. Partly because it transfers employees to the new GTA.