The trash removal system always runs for exactly 0.1ms even if there is only a single grid in it, because it will just keep repeatedly processing that single grid over and over again until it has spent 0.1ms.

This 0.1ms should be definition configurable, and it should never process the same grid twice in a single frame. Practically it would probably be reasonable to limit the per frame grids scanned to 1/100th the total grid count. There's no reason to process grids more than once every few seconds.