endTime 
  The end of the time interval for which to get metric data.
Constraints:
- Specified in Coordinated Universal Time (UTC). 
- Specified in the Unix time format.For example, if you wish to use an end time of October 1, 2018, at 9 PM UTC, specify - 1538427600as the end time.
You can convert a human-friendly time to Unix time format using a converter like Epoch converter.