When doing a math operation to a date command it appear to process the timezone differently.
The system is Ubuntu 18.04.2 LTS. Versions: coreutils/bionic,now 8.28-1ubuntu1 amd64 [installed] #echo $datNow 2019-06-25 15:21:34 #date -d "$datNow " "+%Y-%m-%d %H:%M:%S" --debug date: parsed date part: (Y-M-D) 2019-06-25 date: parsed time part: 15:21:34 date: input timezone: system default date: using specified time as starting value: '15:21:34' date: starting date/time: '(Y-M-D) 2019-06-25 15:21:34' date: '(Y-M-D) 2019-06-25 15:21:34' = 1561501294 epoch-seconds date: timezone: system default date: final: 1561501294.000000000 (epoch-seconds) date: final: (Y-M-D) 2019-06-25 22:21:34 (UTC) date: final: (Y-M-D) 2019-06-25 15:21:34 (UTC-07) 2019-06-25 15:21:34 #date -d "$datNow + 1 minute" "+%Y-%m-%d %H:%M:%S" --debug date: parsed date part: (Y-M-D) 2019-06-25 date: parsed time part: 15:21:34 UTC+01 date: parsed relative part: +1 minutes date: input timezone: parsed date/time string (+01) date: using specified time as starting value: '15:21:34' date: starting date/time: '(Y-M-D) 2019-06-25 15:21:34 TZ=+01' date: '(Y-M-D) 2019-06-25 15:21:34 TZ=+01' = 1561472494 epoch-seconds date: after time adjustment (+0 hours, +1 minutes, +0 seconds, +0 ns), date: new time = 1561472554 epoch-seconds date: timezone: system default date: final: 1561472554.000000000 (epoch-seconds) date: final: (Y-M-D) 2019-06-25 14:22:34 (UTC) date: final: (Y-M-D) 2019-06-25 07:22:34 (UTC-07)