Loading data with day (not timestamp)

Hi Druid users,
My data has only day in YYYY-MM-DD format. How can I use

timestampSpec {} to accommodate that ??

Or do I need to have a timestamp upto the millisecond/second.

If not possible then what are my options with this data?

Thanks,

-Vinay

I got this working by providing

“timestampSpec” : {

        "format" : "YYYY-MM-dd",

        "column" : "event_date"

      }

thx