Subtracting 2.minutes from 12:02:00 AM results in 23:01:00 of the previous day... yet subtracting 120.seconds correctly results in 12:00:00. Also, subtractiong 2.hours from 2:00:00 AM results in the previous day... yet subtracting 7200.seconds correctly results in 12:00:00 Here is the code of two test cases that show the error. The commented out lines should be passing. void testDurationArithmeticOnMinutes() { use(TimeCategory) { def midnight = new Date(100, 0, 1, 0, 0, 0) def oneMinutePastMidnight = new Date(100, 0, 1, 0, 1, 0) def twoMinutesPastMidnight = new Date(100, 0, 1, 0, 2, 0) assert (midnight + 1.minute) == oneMinutePastMidnight assert (midnight + 2.minutes) == twoMinutesPastMidnight assert (twoMinutesPastMidnight - 60.seconds) == oneMinutePastMidnight //assert (twoMinutesPastMidnight - 1.minute) == oneMinutePastMidnight //todo: this should work but fails assert (twoMinutesPastMidnight - 120.seconds) == midnight //assert (twoMinutesPastMidnight - 2.minutes) == midnight //todo: this should work but fails } } void testDurationArithmeticOnHours() { use(TimeCategory) { def midnight = new Date(100, 0, 1, 0, 0, 0) def oneAM = new Date(100, 0, 1, 1, 0, 0) def twoAM = new Date(100, 0, 1, 2, 0, 0) assert (midnight + 1.hour) == oneAM assert (midnight + 2.hours) == twoAM assert (twoAM - 3600.seconds) == oneAM //assert (twoAM - 1.hour) == oneAM //todo: this should work but fails assert (twoAM - 7200.seconds) == midnight //assert (twoAM - 2.hours) == midnight //todo: this should work but fails } }