When I save a Maintenance Event the seconds field of Active Time is set to the minute field automatically.
(Mango 4 beta 12)

    {
      "activeMinute": 55,
      "inactiveMinute": 0,
      "inactiveSecond": 0,
      "activeSecond": 55,
      "activeHour": 0,
      "dataSourceXids": [
        "DS_7c53a913-54e4-4850-a83a-6cd5aaa1978b",
        "DS_59050193-90d0-4232-a93d-9605c5f1c908"
      ],
      "activeMonth": 7,
      "inactiveYear": 2018,
      "togglePermission": [],
      "xid": "ME_10638051-41db-431a-9d26-66e6ad0ff61c",
      "scheduleType": "DAILY",
      "activeYear": 2018,
      "inactiveCron": "",
      "activeCron": "",
      "alias": "ME_Restart_Balance_204",
      "activeDay": 0,
      "alarmLevel": "INFORMATION",
      "disabled": false,
      "inactiveDay": 0,
      "inactiveMonth": 7,
      "inactiveHour": 1
    }

Thanks