How to download hourly forecast variables from 'reanalysis-era5-complete'?

I want to download some forecast variables that are not contained in the 'reanalysis-era5-single-levels'. But I am not sure how the cds-api script has to look like.

For instance, to download hourly wind stress in u-direction for one year (1999) I use is this script:

reanalysis-era5-complete
{ "class": "ea",
"dataset": "era5",
"date": "1999-01-01/to/1999-12-31",
"expver": "1",
"format": "grib",
"grid": "0.25/0.25",
"levtype": "sfc",
"param": "169.128",
"step": "1/to/12/by/1",
"stream": "oper",
"time": "06:00:00/18:00:00",
"type": "fc" }

Is this the correct way and is it also correct that the first 6h are missing? (it will also download the first 6h of the next year). 

Thanks for any help and advise,
Oliver