1a. Brahma's day in strict cyclical parity - rather longer for you ! (5)
Is it CALPA ( which is in the sentence ) of the more used spelling KALPA ?
4a. Judge, setting his heart first, hands out admonitions (2-4) -I/-A--
2d. A jolly old king in charge of Brittany (7) A---R-C
26a. Enough Shakespeare ! (5) -E-T-
n. In Hindu chron., a day of Brahma, a period of 4,320,000,000 years, equivalent to a thousand great ages (mahāyuga); an eon. At the end of the eon, the cosmos is resolved again into chaos, and has to be created anew at the end of another like period, constituting a night of the Supreme Being. Also spelled calpa.