I'm creating various artificial Time Bubbles in my universe where time flows faster or slower inside a specified area, typically depicted as a semi-transparent bubble. Before developing any more stories with this feature I need to figure out any hypothetical size constraints.
The bubbles I am after typically do not cause any catastrophic local damage when activated or later deactivated. A little local damage is acceptable. Extinction level events or even city killers are not. Currently, I have only created "small" Time Bubbles on planets, and haven't yet created anything larger than a small hamlet or out in space.
Aside from the varying amounts of energy I assume, I will require (derived from my Unobtainium using applied Phlebotinum), are there any theorized size constraints to having different sized Time Bubbles? If I need to handwave something, I need to have some idea of what it is, right?
I was curious if, at larger/smaller scales, the square-cube law and other parameters would cause the bubble to break down and collapse, OR cause too much catastrophic damage to the surrounding environments. I don't want to accidentally create a black-hole or blast any of my cities with Gamma-rays or accidentally nuke them into smithereens.
Disclaimer: I know that Time Bubbles are hypothetical and that the real answer is "we don't/can't know". I'm looking for answers derived from current theories, both science and science fiction. As I'm not looking for answers in how to create a Time Bubble, I do not see any magic being involved. If there are no current theories about size restrictions, aside from the previously mentioned energy requirements, great! Please do let me know.