Transformation Points (these used for using Transformation, not the AP counterpart) regens over time (slowly) and is gained by finishing battles. Finishing any single-boss short battle (such as ex-raids) grant 7 points. However, longer/multi-boss battles grant up to 20 points. I am unsure of how it calculates, perhaps based off the same criteria as TP (the AP counterpart)/old transfo exp - the more you fight and kill, the more You get up to 110 TP.
Current transformation design seems useful for doing S3 dailies: transf at the beginning, the +5 seconds per mob kill will allow You to keep transformation until boss stage. Then, once You reach ~55 seconds remaining in transformation - use second transfo for extra damage.