This extension does indeed do as announced, no patron paywalls, no weird bugs, no strange messaging, no playlist size limitations. Excelent work! (Just be aware it takes a long while to compute the sort, probably because it accesses youtube to verify it's actually working on every step)

This is it! This is the one! It ACTUALLY sorts your 1000+ video long watch later playlist by duration! For free! Holy moly! Thank you!