I mean how fast will they be disintegrated? How far from the Bryozoan reef will they be in less then a millimeter in size? Do you know any experiment concerning this subject?
Your question is a fundamental and the answer depends on an understanding the local/regional palaeogeography, water depth and energy levels. By subaquatic, I assume that you looking at sediment buildup and transport. My experience is that millimetric packstones and grainstones can be accumulated downslope over 1-2 kilometres. Bioturbation if likely can speed up the process of fragmentation.
Maceration, picking and observation under microscope and SEM these are the routine methods to understand as I understand. May have more advance metohds, someone who know it please add here.