[css-color-3] CR SoTD needs: expected duration of the CR period

[tantek]

Per transition approval on behalf of the Director, the new CSS3 Color CR needs an explicit expected duration of the CR period in the SoTD before being published. cc: @svgeesus @dbaron

[tantek]

Per https://www.w3.org/2017/Process-20170301/#candidate-rec

the deadline for comments, which must be at least four weeks after publication

The four weeks minimum is sufficient (and likely was the default intent of the WG resolution to go to CR) since the changes are fairly minor for this REC->CR->ER.

Earliest possible publication is next Tuesday 2017-12-05. Four weeks after that is 2018-01-02.

If anyone believes more time is necessary, please comment!