It does not matter. Each tick you spawn some (thousands) of HISMs, this will go as fast as it can while still maintaining a degree of responsiveness. You can set the tick to any value anyway. This was just a test to see if we can go above 1m, we absolutely can provide we spread the spawning over time and not force the engine to create too many in a single tick.
You could use a timer but then we will not go as fast as we can - it will be more controlled, though.
Is there an upper limit of how many HISMs UE can actually handle?
Probably. But the idea is to spawn chunks around the player and then get rid of them when they move away.
I am assuming you’re familiar with: