Tl;dr: release the last Wednesday of June, RC2 two weeks prior; RC1 three weeks prior to RC2. Looks like this schedule works well. Same logic as usual - post-RC2 only the fixes for issues found in CSIT, post-RC1 only the fixes + specially agreed low risk commits.
This kind of schedule seems to have worked pretty well, so I will keep it, unless there’s anyone tells a good reason not to.