Living material, where the only number that matters at the end is how much of it is still alive. Every other consideration in the cycle is subordinate to that.
A cycle that finishes six hours faster and loses a log of viability has not saved anything.
Cells are stressed at three points: freezing, primary drying, and storage. Freeze rate governs ice crystal size, and ice crystal size governs mechanical damage to cell membranes. Too slow and large crystals form and puncture; too fast and other problems appear. That rate is a developed parameter, not a default.
Cryoprotectants and the carrier matrix do much of the protective work, which means the formulation and the cycle have to be developed together rather than sequentially.
Culture slurries typically have low collapse temperatures, which caps the heat available and therefore the speed.
Exceed it and the cake collapses, taking the porous structure and often the viability with it. It does not recover. The practical consequence is that these cycles are long by physics, and any supplier promising a short one is promising something the material will not do.
Chamber pressure control matters more here than in most food work, because pressure and product temperature are coupled and the margin above collapse is narrow.
Secondary drying decides how long the product survives storage.
Too much residual moisture and viability falls off through shelf life. Too aggressive a secondary and you damage the cells you protected through primary. The target is a range, established for the specific organism and matrix, and verified by assay rather than assumed.
Culture and probiotic cycle references from operating data. [SPEC — Nick to confirm] Note: these are commercial production systems, not validated pharmaceutical equipment.