You can run the skel mesh primary tick whenever you like but you’ll have to live with the potential side effects of moving it. As you mention, if you allow the tick to complete after PrePhysics finishes (to allow DuringPhysics to kick in potentially before you run), then you might run concurrently with physics and the order of execution isn’t guaranteed. This means that on some frames you might run before and have no latency (same as finishing in PrePhysics) while other frames you might run after physics and introduce a frame of delay. This could change frame to frame with the potential to do bad things as the change in momentum might become erratic on the rigid bodies impacted by your skel mesh. If you want determinism, you’ll want to make sure you complete before physics kicks off or you have to run after physics is done, consistently.
That being said, this lack of determinism with respect to the physics simulation might not matter in your case, at least for Chaos cloth. If you drive rigid bodies that can impact the main physics scene (e.g. you can push ragdolls or env things) then the lack of determinism is potentially problematic. However, Chaos cloth uses a local simulation by default (I think) as it doesn’t collide with the environment (and other things in the main physics scene). I believe it only self-collides by default and as such you only need cloth to run after the skeletal mesh and either of these could happen at any time in the frame. You can think of Chaos cloth as running its own physics scene where you have to specify what to include explicitly for each instance.