Javascript time calculations in custom reports aka more problems using rest api as a dataset

So, 

I am creating a report to capture events across time.

The problem is that the daterange input control returns time as a UTC string, but the api wants epoch time.

The input looks like this, and it passes the correct data but 

I tried just sticking Date.parse in there, but it didn’t work.

Is there a way to massage the output of the controls before using them as inputs?

With sql as a data source you can handle it all the query.

Can someone tell me what I am missing?

Thanks.

Chris.