Ten Seconds per Texture
The ear/brain needs about ten seconds to adjust to and digest a new musical texture so changing orchestration colours roughly in that tempo is something that feels quite natural/interesting and is easy to digest for our brain. However using that knowledge you can also create feelings of haste or slowness just with the pace of how often you change the texture.
Very quickly switching between colours and structures will feel frenetic and hasty which is great in action and comedy scoring while staying very long in one texture can feel calm, relaxed and edging to boring. Using that guideline will also give you a good idea whether you’re just starting to over-orchestrate or might be just a tad too long in the same colour. As usual, it is a rule of thumb and highly depending on each individual, but as a rough guideline, the ten second rule is quite useful.