瑜伽師地論略纂 8.136

8.136

論云「於其所作成辨時轉」者，謂所成辨，彼所依清淨；所依清淨故，令遍滿、愛樂清淨：故言成辨時轉。

Where the treatise says, "it operates at the time when that which was to be accomplished is accomplished," it means that what was to be accomplished has its basis purified; because the basis is purified, it causes pervading and rejoicing to be purified; hence it says "it operates at the time of accomplishment."