If you want to stay top of mind for a constantly growing audience and increase visibility, post every day.
If you want to amplify your launch, focus on the period before, during, and after the launch.
Before the launch, I would start with enough time in advance, around one month before, and I would personally post approximately (at least) twice a week.
But I think that in general, if you want to be visible within the forums, twice a week is bearable.
