The Instancing is dynamic even in normal Space, unsure of its radius. It was mentioned in some very old Dev Livestream. 40-50km? Unsure, forgot.
They also explained why and how Instances involving i.e. the SRV were a little different, how Speed mattered and stuff.
So if you take a break i.e. 490km from a Hotspot Center and another Miner just happens to travel your way from that Center - eventually you'll get instanced dynamically (within the P2P limitations) - just as well as you'd get de-instanced again if the Distance to the other Player increases beyond a certain limit again.
Chances of this happening is quite low due to the distances - but should you operate i.e. in one of the more famous Double-Painite Hotspots, the chances aren't so bad actually.
I kinda assume that the question comes from "I take several breaks during bigger Mining sessions but don't want to log to Menu because of NPC spawns after re-logging".
It's a tradeoff, especially in Open. But chances of another Miner detecting your Ship AND going Hostile for no need (more than enough Asteroids after all) seems very low to me.
In such cases, likely best to avoid moving on a line directly from one Hotspot center to another, rather offset it by >100km to be on the safe side.