What is the output of these two logs?
GPS date string: 2017/05/15 09:33 1494865998000
Sys date string: 2017/05/15 09:31 1494865897600
GPS date string: 2017/05/15 09:33 1494865998000
Sys date string: 2017/05/15 09:31 1494865898600
GPS date string: 2017/05/15 09:33 1494865998000
Sys date string: 2017/05/15 09:31 1494865899600
GPS date string: 2017/05/15 09:33 1494865998000
Sys date string: 2017/05/15 09:31 1494865900600
GPS date string: 2017/05/15 09:33 1494865998000
Sys date string: 2017/05/15 09:31 1494865901600
GPS date string: 2017/05/15 09:33 1494865998000
Sys date string: 2017/05/15 09:31 1494865902600
GPS date string: 2017/05/15 09:33 1494865998000
Sys date string: 2017/05/15 09:31 1494865903601
GPS date string: 2017/05/15 09:33 1494865998000
Sys date string: 2017/05/15 09:31 1494865904601