瑜伽師地論略纂 1.94

1.94

劫時節中，唯二十住劫有增有減，可說二十；成、壞、空三既無增減，准住劫量。初禪壽量中，梵前益天者，即是第二梵輔天也，大梵王前作饒益故。

Regarding the kalpa periods: only the twenty kalpas of staying have increase and decrease, so twenty can be spoken of; since the three kalpas of formation, destruction, and emptiness have neither increase nor decrease, they are measured according to the duration of a kalpa of staying. In the lifespans of the first dhyāna, the "devas who benefit in front of Brahmā" are the second, the Brahmapurohita devas, because they perform beneficent service before the Great Brahmā King.