3-4 months between changes.
4-6 weeks is the minimum for changes when first starting and while still figuring out correct diopters. If we’re using diopters as part of ongoing improvement, reducing sooner than 3-4 months is not usually productive.
You can reduce one first (up to you, normalized or differential) then the other 4-6 weeks later.
Also see pro topic video Normalized – Differential – Normalized.