The limit is set by your clarification technique (typically a strainer). As long as you can strain the pieces of mirepoix out at the end, the resulting stock can be as rich and clear as any you have ever made, but it can also be ready in a fraction of the typical time. Our recipes typically call for chopping bones or sawing them into 5 cm / 2 in pieces, if possible. The interior of bone is quite porous, so bone fragments have a high ratio of surface area to volume, and flavors thus diffuse from them a rate similar to that of much smaller pieces of less porous food (such as meat).